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Percentage Concentration to Molarity Calculator

Ready to calculate
M = % × ρ × 10 / MW.
13 reagent presets.
Custom MW supported.
100% Free.
No Data Stored.

How it Works

01Pick a Solution Preset

13 common reagents pre-loaded (HCl, H₂SO₄, NH₃, NaOH, etc.) or pick custom and enter any MW.

02Enter Density and Percentage

Density in g/cm³ (= g/mL) from supplier datasheet; mass percent w/w from the bottle label.

03Apply M = % × ρ × 10 / MW

Standard conversion: 37% HCl × 1.19 g/cm³ × 10 / 36.46 g/mol = 12.07 M.

04Get Molarity + Mass Conc.

Output in M / mM / µM, plus mass concentration in g/L = mg/mL for cross-checking.

What is a Percentage Concentration to Molarity Calculator?

Concentrated reagents — HCl, H₂SO₄, NaOH, NH₃, HNO₃ — come from suppliers labeled by mass percent (% w/w), not molarity. "37% HCl" means 37 grams of HCl per 100 grams of solution. But every quantitative chemistry workflow (titration, dilution, stoichiometry, kinetics) uses molarity (mol/L), so the first step in working with any concentrated reagent is always converting % to M. Our Percentage Concentration to Molarity Calculator implements the standard conversion: M (mol/L) = (% × ρ × 10) / MW, where % is the mass percent (w/w) from the bottle label, ρ is the solution density in g/cm³, and MW is the molar mass in g/mol.

The calculator includes 13 common reagent presets with auto-filled molar masses, eliminating the most common error source (using the wrong MW): Ammonia 17.03, Acetic acid 60.05, Ethanol 46.07, Formaldehyde 30.03, Glucose 180.16, Hydrochloric acid 36.46, Hydrogen peroxide 34.01, Nitric acid 63.01, Phosphoric acid 98.00, Potassium hydroxide 56.11, Sodium chloride 58.44, Sodium hydroxide 40.00, and Sulfuric acid 98.08 g/mol. For any compound not in the list, "Set custom molar mass" mode lets you enter the MW directly. Density input accepts g/cm³, g/mL, kg/L, or kg/m³.

Output: molarity in M / mM / µM simultaneously plus the equivalent mass concentration in g/L (= mg/mL) for cross-checking. The result panel shows the full transparent calculation breakdown: input quantities → mass concentration → moles → molarity. Smart warnings catch unphysical values (MW < 1 g/mol or > 1 MDa, density < 0.5 or > 5 g/cm³) and unrealistic concentrations beyond saturation limits (M > 30 mol/L). Designed for analytical chemists preparing working solutions from concentrated stocks, biochemists making buffer dilutions, organic chemists scaling up reactions from supplier specs, students learning stoichiometric conversions, and anyone needing a fast bottle-label-to-molarity conversion — runs entirely in your browser, no account, no data stored.

Pro Tip: Pair this with our Molarity Calculator for forward calculations, our Dilution Factor Calculator for serial dilution, our Molality Calculator for colligative-property work, or our Mass Percent Calculator for the reverse conversion.

How to Use the Percentage Concentration to Molarity Calculator?

Pick a Solution Preset OR Use Custom MW: 13 common reagents pre-loaded with auto-filled molar mass — Ammonia, Acetic acid, Ethanol, Formaldehyde, Glucose, HCl, H₂O₂, HNO₃, H₃PO₄, KOH, NaCl, NaOH, H₂SO₄. For any other compound, pick "Set custom molar mass" and enter MW manually.
Confirm or Edit the Molar Mass: the preset MW is the anhydrous form. Critical: if your bottle is a hydrate (e.g. CuSO₄·5H₂O, MgSO₄·7H₂O), use the hydrate MW — using the wrong form gives 30-50% errors. Verify against the bottle label's "·nH₂O" notation.
Enter the Density of the Solution: in g/cm³, g/mL (numerically equal), kg/L (numerically equal), or kg/m³. Density depends on concentration — use the value at YOUR exact concentration from the supplier datasheet or CRC Handbook density tables. Examples: 37% HCl ρ = 1.19 g/cm³; 70% HNO₃ ρ = 1.42; 98% H₂SO₄ ρ = 1.84; 50% NaOH ρ = 1.52; 28% NH₃ ρ = 0.90.
Enter the Mass Percent (% w/w): from the bottle label. "% w/w" means grams of solute per 100 g of solution, NOT per 100 g of solvent. For example, "37% HCl" = 37 g HCl + 63 g water = 100 g solution.
Apply M = (% × ρ × 10) / MW: The calculator automates the conversion. Algebraic derivation: in 1 L of solution, total mass = ρ × 1000 mL = 1000ρ grams; solute mass = (%/100) × 1000ρ = 10·%·ρ g; moles = (10·%·ρ) / MW; per L gives molarity in mol/L.
Read Molarity in 3 Unit Prefixes: M (mol/L), mM (mmol/L = 10⁻³ M), µM (µmol/L = 10⁻⁶ M). Pick whichever your downstream calculation or protocol uses.
Cross-Check with Mass Concentration: the result panel also shows g/L (= mg/mL); useful for verifying against clinical or environmental concentration units. Verify against canonical values: 37% HCl → 12.07 M; 70% HNO₃ → 15.78 M; 98% H₂SO₄ → 18.38 M; 50% NaOH → 19.00 M; 28% NH₃ → 14.80 M.

How is percentage to molarity calculated?

Converting % w/w to molarity is the first step in working with any concentrated commercial reagent. The math is straightforward; getting the density right at your exact concentration is the most common source of error.

References: CRC Handbook of Chemistry and Physics; supplier (Sigma-Aldrich, Fisher, VWR) reagent datasheets; IUPAC Compendium of Chemical Terminology.

Core Formula

M (mol/L) = (% × ρ × 10) / MW

Where % is mass percent (w/w), ρ is solution density in g/cm³ (= g/mL), and MW is molar mass in g/mol. The factor 10 comes from converting (1 g/cm³ → 1000 g/L) × (1/100 from %) = 10.

Algebraic Derivation

  • Consider 1 L = 1000 mL of solution.
  • Mass of solution = ρ × 1000 mL = 1000ρ grams.
  • Mass of solute = (%/100) × 1000ρ = 10·%·ρ grams.
  • Moles of solute = mass / MW = (10·%·ρ) / MW.
  • Molarity = moles per liter = (10·%·ρ) / MW mol/L.

Worked Example — Concentrated HCl

Bottle label: 37% w/w HCl, density 1.19 g/cm³. MW(HCl) = 36.46 g/mol.

  • M = (37 × 1.19 × 10) / 36.46 = 440.3 / 36.46 = 12.07 mol/L = 12.07 M.
  • Mass concentration = 37 × 1.19 × 10 = 440.3 g/L.
  • This is the canonical "12 M HCl" used as the lab concentrated stock.

Worked Example — Concentrated H₂SO₄

Bottle label: 98% w/w H₂SO₄, density 1.84 g/cm³. MW(H₂SO₄) = 98.08 g/mol.

  • M = (98 × 1.84 × 10) / 98.08 = 1803.2 / 98.08 = 18.38 mol/L = 18.38 M.
  • Mass concentration = 1803.2 g/L.
  • This is the canonical "18 M H₂SO₄" used as the lab concentrated stock; produces enormous heat on dilution — always add acid TO water.

Worked Example — Aqueous Ammonia

Bottle label: 28% w/w NH₃ (aqueous ammonia), density 0.90 g/cm³. MW(NH₃) = 17.03 g/mol.

  • M = (28 × 0.90 × 10) / 17.03 = 252 / 17.03 = 14.80 mol/L = 14.80 M.
  • Often labeled "concentrated ammonia" or "ammonium hydroxide"; is volatile and loses ammonia over time when not properly sealed (concentration drops with bottle age).

Common Concentrated Reagents (Reference Values)

  • HCl, 37% w/w, ρ 1.19: 12.07 M.
  • HBr, 48% w/w, ρ 1.49: 8.84 M.
  • HI, 57% w/w, ρ 1.70: 7.57 M.
  • HNO₃, 70% w/w, ρ 1.42: 15.78 M.
  • HNO₃, fuming 90% w/w, ρ 1.50: 21.4 M.
  • H₂SO₄, 98% w/w, ρ 1.84: 18.38 M.
  • HClO₄, 70% w/w, ρ 1.66: 11.54 M.
  • H₃PO₄, 85% w/w, ρ 1.69: 14.66 M.
  • Glacial acetic acid, 99.7% w/w, ρ 1.05: 17.42 M.
  • Formic acid, 88% w/w, ρ 1.20: 22.94 M.
  • NaOH, 50% w/w, ρ 1.52: 19.00 M.
  • KOH, 45% w/w, ρ 1.46: 11.71 M.
  • NH₃ aq, 28% w/w, ρ 0.90: 14.80 M.
  • H₂O₂, 30% w/w, ρ 1.11: 9.79 M.
  • H₂O₂, 50% w/w, ρ 1.20: 17.65 M.

The Inverse Conversion (Molarity → %)

% w/w = (M × MW) / (10 × ρ)

Useful when you have a target molarity and want to know what mass-percent bottle to order. Example: 1.0 M aqueous NaOH, ρ ≈ 1.04 → % = (1.0 × 40) / (10 × 1.04) = 3.85% w/w.

Real-World Example

Worked Example — Make 1 L of 1 M NaOH from 50% Stock

Question: The lab has a stock bottle labeled "50% w/w NaOH (sodium hydroxide), density 1.52 g/cm³." How do I make 1 L of 1.0 M NaOH from this stock?

Step 1 — Compute the Stock Molarity.

  • MW(NaOH) = 40.00 g/mol.
  • M_stock = (50 × 1.52 × 10) / 40.00 = 760 / 40.00 = 19.0 M NaOH.

Step 2 — Compute the Dilution. Use C₁V₁ = C₂V₂.

  • C₁ = 19.0 M (stock); C₂ = 1.0 M (target); V₂ = 1000 mL (target volume).
  • V₁ = (C₂ × V₂) / C₁ = (1.0 × 1000) / 19.0 = 52.6 mL of 50% NaOH stock.

Step 3 — Procedure.

  • To a 1 L volumetric flask, add about 700 mL of distilled water.
  • Slowly add 52.6 mL of 50% NaOH stock (use a calibrated graduated cylinder; concentrated NaOH is highly caustic — wear PPE).
  • Swirl gently; the dissolution is exothermic so let cool to room T before final adjustment.
  • Top up to 1.000 L mark with distilled water; stopper and invert 10-20 times to mix.
  • Label: "1.0 M NaOH, [date], [initials]."

Step 4 — Verify.

  • Predicted moles in final solution: 52.6 mL × 19.0 M / 1000 = 1.000 mol.
  • In 1 L: 1.000 mol/L = 1.0 M ✓.
  • For high-precision titration use, standardize the prepared solution against potassium hydrogen phthalate (KHP) — atmospheric CO₂ absorption can reduce effective NaOH concentration over time.

Step 5 — Safety.

  • 50% NaOH is extremely caustic — causes severe skin burns and eye damage on contact.
  • Always add NaOH to water (never water to concentrated NaOH; the heat-of-dilution can cause violent splashing of caustic solution).
  • PPE: lab coat, full face shield, neoprene/nitrile gloves, closed-toe shoes.
  • Spill response: dilute with copious water; do NOT use acid to neutralize a NaOH spill (exothermic, splashing hazard).

Who Should Use the % → Molarity Calculator?

1
Convert bottle-label % to molarity, then use C₁V₁ = C₂V₂ to compute the stock volume needed for a target working concentration. The most-common workflow for making working solutions from concentrated reagents.
2
Prepare standardized solutions for titration, calibration curves, and quantitative analysis. Combine % conversion with primary-standard verification (KHP for NaOH, oxalic acid for KMnO₄, etc.).
3
Many biochemistry buffers start from concentrated stocks (HCl, NaOH for pH adjustment; H₂O₂ for oxidative assays; concentrated salt solutions). Quick % → M conversion sets the dilution.
4
Compounding pharmacists work with USP-grade concentrated reagents (HCl, NH₃, ethanol) labeled by % w/w; convert to molarity for dose-volume calculations.
5
Industrial reagent suppliers (Sigma-Aldrich, Fisher, VWR, Acros) ship concentrates labeled by % w/w; process engineers convert to molar units for material-balance and reactor-design calculations.
6
Standard general-chemistry textbook problem — compute molarity of concentrated HCl/H₂SO₄/NaOH from supplier specs. The calculator handles arithmetic; students focus on understanding the conversion.
7
Convert trace contaminant concentrations between % (regulatory limits) and molarity (chemistry equations) for water-quality, soil, and air-pollution assessments.

Technical Reference

The Conversion Formula and Its Derivation. The relationship M = (% × ρ × 10) / MW arises from dimensional analysis. Consider 1 L of solution: total mass = ρ × 1000 mL = 1000·ρ grams (where ρ is density in g/cm³). The mass of solute = (%/100) × 1000·ρ = 10·%·ρ grams. Moles of solute = (10·%·ρ) / MW (where MW is in g/mol). Molarity = moles per liter = (10·%·ρ) / MW. The 10 factor combines the 1000 (g/cm³ × mL → g/L) and 1/100 (% → fraction) factors: 1000/100 = 10.

Density Dependence on Concentration. For aqueous solutions, density rises with solute concentration in a smooth but non-linear way. HCl: 10% w/w 1.048 g/cm³; 20% 1.098; 30% 1.149; 37% 1.190. H₂SO₄: 10% 1.066; 30% 1.219; 50% 1.395; 70% 1.610; 90% 1.814; 98% 1.840 (max ~1.842 at 99%). NaOH: 10% 1.109; 25% 1.274; 50% 1.524. HNO₃: 10% 1.054; 30% 1.180; 50% 1.310; 70% 1.413; 90% 1.483. Always use the density at YOUR exact concentration — using a generic value introduces 5-15% error.

Temperature Dependence. Density decreases with increasing temperature (~0.05% per °C for typical aqueous reagents). Molarity also drifts slightly with T because volume changes (~0.5% drop per 10 °C rise). For routine work at controlled lab T (20-25 °C), the correction is negligible; for high-precision NIST-traceable work, specify and control T to ±0.1 °C and use density tables at the exact T.

Common Concentrated Lab Reagents (Reference Table).

  • Hydrochloric acid (HCl): 37% w/w, ρ 1.190 g/cm³, MW 36.461 → 12.07 M.
  • Hydrobromic acid (HBr): 48% w/w, ρ 1.490 g/cm³, MW 80.911 → 8.84 M.
  • Hydroiodic acid (HI): 57% w/w, ρ 1.70 g/cm³, MW 127.91 → 7.57 M.
  • Nitric acid (HNO₃): 70% w/w, ρ 1.413 g/cm³, MW 63.013 → 15.69 M; fuming 90% ρ 1.503 → 21.46 M.
  • Sulfuric acid (H₂SO₄): 98% w/w, ρ 1.840 g/cm³, MW 98.079 → 18.38 M; oleum (fuming) ρ 1.94+ depending on % SO₃.
  • Perchloric acid (HClO₄): 70% w/w, ρ 1.660 g/cm³, MW 100.46 → 11.56 M.
  • Phosphoric acid (H₃PO₄): 85% w/w, ρ 1.685 g/cm³, MW 97.995 → 14.62 M.
  • Glacial acetic acid (CH₃COOH): 99.7% w/w, ρ 1.049 g/cm³, MW 60.052 → 17.42 M.
  • Formic acid (HCOOH): 88% w/w, ρ 1.197 g/cm³, MW 46.025 → 22.89 M; 99% ρ 1.221 → 26.27 M.
  • Sodium hydroxide (NaOH): 50% w/w, ρ 1.524 g/cm³, MW 39.997 → 19.05 M.
  • Potassium hydroxide (KOH): 45% w/w, ρ 1.460 g/cm³, MW 56.106 → 11.72 M.
  • Ammonia aqueous (NH₃ aq, "ammonium hydroxide"): 28-30% w/w as NH₃, ρ 0.898-0.910 g/cm³, MW 17.031 → 14.78-16.04 M.
  • Hydrogen peroxide (H₂O₂): 30% w/w, ρ 1.111 g/cm³, MW 34.015 → 9.80 M; 50% ρ 1.196 → 17.59 M; 70% ρ 1.290 → 26.55 M (rocket-grade).

Hydrate vs Anhydrous Reagents. Many crystalline salts come as hydrates with stoichiometric water of crystallization that is part of the formula mass:

  • CuSO₄·5H₂O 249.69 vs anhydrous CuSO₄ 159.61 (+56% mass).
  • FeSO₄·7H₂O 278.01 vs anhydrous 151.91 (+83% mass).
  • MgSO₄·7H₂O 246.47 vs anhydrous 120.37 (+105% mass).
  • Na₂CO₃·10H₂O 286.14 vs anhydrous 105.99 (+170% mass).
  • EDTA·2H₂O·2Na 372.24 vs anhydrous Na₂EDTA 336.21.

Using the wrong form gives 30-100% errors. The MW values in the calculator presets are anhydrous (the chemical compound itself). For hydrate forms, override with the hydrate MW in custom mode.

Density Sources. For research-grade work, use:

  • CRC Handbook of Chemistry and Physics — density tables for binary aqueous solutions of every common reagent.
  • International Critical Tables of Numerical Data, Physics, Chemistry and Technology (vol. III).
  • Supplier datasheets / Certificates of Analysis (CoA) for the specific lot.
  • NIST WebBook for thermophysical-grade data.
  • Software: REFPROP (NIST), CRC Handbook online subscription, Sigma-Aldrich solubility/density database.

The Inverse Conversion (M → %). Sometimes the inverse problem arises: given a target molarity and known density, what % do I need? Rearrange: % = (M × MW) / (10 × ρ). Example: target 1.0 M NaOH; ρ ≈ 1.04 g/cm³ for ~1 M aqueous NaOH; % = (1.0 × 40) / (10 × 1.04) = 3.85% w/w. For dilute aqueous solutions (M < 1 mol/L) where ρ ≈ 1 g/cm³: % ≈ (M × MW) / 10. For 1 M glucose: % ≈ (1 × 180.16) / 10 = 18% w/w. References: CRC Handbook of Chemistry and Physics; supplier (Sigma-Aldrich, Fisher, VWR) reagent datasheets; IUPAC Compendium of Chemical Terminology.

Conclusion

Converting mass percent to molarity is the universal first step in working with concentrated commercial reagents. The math — M = (% × ρ × 10) / MW — is one line. Memorize the canonical reference values: 37% HCl → 12 M; 70% HNO₃ → 16 M; 98% H₂SO₄ → 18 M; 50% NaOH → 19 M; 28% NH₃ → 15 M — and you can quickly check any new bottle's expected molarity in seconds.

Two operational reminders: (1) The most common error is using the wrong density — density varies significantly with concentration (10% HCl ≈ 1.05 g/cm³ vs 37% HCl ≈ 1.19 g/cm³); always use the supplier-specific value for YOUR bottle's exact concentration. (2) The second most common error is hydrate vs anhydrous MW confusion — CuSO₄·5H₂O 249.69 g/mol vs anhydrous CuSO₄ 159.61, MgSO₄·7H₂O 246.47 vs anhydrous 120.37. Always check the bottle for "·nH₂O" notation. For accurate working-solution preparation, follow conversion with C₁V₁ = C₂V₂ dilution math; use a calibrated volumetric flask, not a graduated cylinder, for the final volume adjustment; and always add concentrated acid TO water (never water to concentrated acid) to prevent dangerous heat-of-dilution splashing.

Frequently Asked Questions

What is the Percentage Concentration to Molarity Calculator?
It implements the standard conversion M = (% × ρ × 10) / MW, where % is mass-percent w/w (from bottle label), ρ is solution density in g/cm³, and MW is molar mass in g/mol. 13 reagent presets with auto-filled MW (HCl, H₂SO₄, NaOH, NH₃, etc.) plus custom-MW mode for any compound. Output: molarity in M / mM / µM and mass concentration in g/L.

Pro Tip: Pair this with our Molarity Calculator.

What is the formula for percentage to molarity?
M = (% × ρ × 10) / MW. Where % is the mass-percent w/w (e.g. 37 for 37% HCl), ρ is the density of the solution in g/cm³ (= g/mL; e.g. 1.19 for 37% HCl), and MW is the molar mass in g/mol (e.g. 36.46 for HCl). The factor 10 comes from converting mL to L (× 1000) divided by the % factor (÷ 100). Example: 37% HCl × 1.19 × 10 / 36.46 = 12.07 M.
How do I convert 37% HCl to molarity?
12.07 M. Math: 37% w/w HCl has density ρ = 1.19 g/cm³; MW(HCl) = 36.46 g/mol. M = (37 × 1.19 × 10) / 36.46 = 440.3 / 36.46 = 12.07 mol/L. This is the canonical "12 M HCl" used as the lab concentrated stock. To make 1 L of 1.0 M HCl: V_stock = 1000 / 12.07 = 82.8 mL of concentrated HCl diluted to 1 L with water (always add acid TO water).
How do I convert 98% H₂SO₄ to molarity?
18.38 M. Math: 98% w/w H₂SO₄, ρ = 1.84 g/cm³, MW = 98.08 g/mol. M = (98 × 1.84 × 10) / 98.08 = 1803.2 / 98.08 = 18.38 mol/L. This is the canonical concentrated lab sulfuric acid. Safety: dilution is highly exothermic (~74 kJ/mol); always add concentrated acid TO water in small portions with stirring; never add water to concentrated acid (causes violent splashing).
How do I convert 50% NaOH to molarity?
19.05 M. Math: 50% w/w NaOH, ρ = 1.52 g/cm³, MW = 40.00 g/mol. M = (50 × 1.52 × 10) / 40.00 = 760 / 40.00 = 19.0 mol/L. This is the most concentrated commercially available NaOH solution; lower concentrations exist (32% w/w membrane-grade ρ 1.35 → 10.8 M; 25% ρ 1.27 → 7.94 M). NaOH is highly caustic — handle with full PPE.
What's the molarity of concentrated ammonia?
~14.8 M (28% w/w aqueous NH₃, ρ 0.90 g/cm³). Math: M = (28 × 0.90 × 10) / 17.03 = 14.80 mol/L. Sometimes labeled "ammonium hydroxide" or "NH₄OH" but the actual species in solution is mostly NH₃ in water with a small equilibrium fraction of NH₄⁺ + OH⁻. Volatile: concentrated ammonia loses NH₃ to vapor over time, especially when warmed — actual concentration drops with bottle age and number of openings. Standardize against HCl before use for analytical work.
What's the molarity of concentrated nitric acid?
~15.7 M (70% w/w HNO₃, ρ 1.42 g/cm³). Math: M = (70 × 1.42 × 10) / 63.01 = 15.78 mol/L. Fuming HNO₃ (90% w/w, ρ 1.50): 21.4 M — much more reactive; releases NO₂ vapor on opening. Standard 70% concentrated HNO₃ is used for nitration reactions, oxidation, and as a strong acid; produces toxic NO₂ vapor on heating.
Why does the calculator have so many solution presets?
To eliminate the most common error: using the wrong molar mass. Students and even experienced chemists frequently make MW lookup errors — especially for compounds with multiple common forms (anhydrous vs hydrate, polymorphs, etc.). The 13 presets cover the most common concentrated lab reagents with verified MW values from supplier datasheets. For other compounds, pick "Set custom molar mass" and enter the value from PubChem, CRC Handbook, or your supplier's Certificate of Analysis.
Why is solution density important?
Because density connects mass and volume. The molarity formula needs to convert mass-percent (which is per-gram-of-solution) to per-liter-of-solution; this requires knowing how many grams are in a liter (= ρ × 1000 mL). For pure water, ρ = 1.00 g/cm³, so density barely affects the math. For concentrated reagents like H₂SO₄ (ρ 1.84) or NaOH (ρ 1.52), density adds 50-80% to the molarity vs assuming water density. Use supplier-specific density at YOUR concentration; don't use a generic "1 g/cm³" assumption for concentrated solutions.
How do I find density for an unusual concentration?
Three options. (1) Supplier datasheet — Sigma-Aldrich, Fisher, VWR all publish density tables for their concentrated reagents covering common concentration ranges. (2) CRC Handbook of Chemistry and Physics — has comprehensive density tables for binary aqueous solutions of every common acid, base, and salt at multiple concentrations and temperatures. (3) Direct measurement — pycnometer (calibrated bottle, weigh full minus empty), vibrating-tube densitometer (Anton Paar etc., ±0.0001 g/cm³ precision), or hydrometer (±0.5%). Online resources: Anton Paar density calculator, Sigma-Aldrich density tools.
What's the inverse conversion (molarity to %)?
% = (M × MW) / (10 × ρ). Useful when you know the target molarity and want to know what bottle to order. Example: 1.0 M aqueous NaOH, ρ ≈ 1.04 g/cm³ for ~1 M aqueous → % = (1.0 × 40) / (10 × 1.04) = 3.85% w/w. For dilute aqueous solutions (M < 1 mol/L) where ρ ≈ 1 g/cm³: % ≈ (M × MW) / 10 as a quick mental approximation. For 1 M glucose: % ≈ 18%; for 1 M NaCl: % ≈ 5.8% — these are the sort of values you would see on supplier-prepared standard solutions.

Author Spotlight

The ToolsACE Team - ToolsACE.io Team

The ToolsACE Team

Our ToolsACE chemistry team built this calculator to handle the standard <strong>% w/w to molarity</strong> conversion used in every analytical-chemistry laboratory worldwide. The defining identity is <strong>M (mol/L) = (% × ρ × 10) / MW</strong>, where % is the mass percent (w/w from the bottle label), ρ is the solution density in g/cm³ (= g/mL), and MW is the molar mass in g/mol. The calculator includes <strong>13 common reagent presets</strong> with auto-filled molar masses — Ammonia (17.03), Acetic acid (60.05), Ethanol (46.07), Formaldehyde (30.03), Glucose (180.16), Hydrochloric acid (36.46), Hydrogen peroxide (34.01), Nitric acid (63.01), Phosphoric acid (98.00), Potassium hydroxide (56.11), Sodium chloride (58.44), Sodium hydroxide (40.00), and Sulfuric acid (98.08) — plus a custom-MW mode for any other compound. Density input accepts g/cm³, g/mL, kg/L, or kg/m³ for international units flexibility. Output: molarity in M / mM / µM and mass concentration in g/L (= mg/mL) with full transparent breakdown.

Standard analytical chemistry references; CRC Handbook of Chemistry and PhysicsSupplier-aligned molar masses (Sigma-Aldrich, Fisher, VWR datasheets)IUPAC concentration definitions

Disclaimer

The conversion M = (% × ρ × 10) / MW assumes you know the correct density at YOUR concentration. Density varies significantly with concentration (10% HCl ρ ~1.05 vs 37% HCl ρ ~1.19) — always use the supplier-specific density for your bottle's exact concentration. CRC Handbook density tables cover most aqueous reagents. The MW values in the preset list are anhydrous; for hydrate forms (CuSO₄·5H₂O 249.69 vs anhydrous 159.61) use the form on YOUR bottle label. Strong acids and bases generate heat on dilution — always add concentrated acid TO water (not water to acid) and use heat-resistant glassware. References: CRC Handbook of Chemistry and Physics; supplier (Sigma-Aldrich, Fisher, VWR) reagent datasheets; IUPAC Compendium of Chemical Terminology.