Amp to Wire Size Calculator
How it Works
01Pick Amps
15, 20, 30, 40, 50, 60, 100, 125, 150, 200 amp presets — or any custom value.
02Voltage & Type
120V, 240V, 480V — single-phase, three-phase, or DC.
03Length
One-way from panel to load. 100 ft is typical branch.
04AWG From Amps
Recommended AWG with both ampacity AND voltage drop satisfied.
What is an Amp to Wire Size Calculator?
An amp to wire size calculator converts any amperage — 5A to 400A, residential to commercial — into the correct AWG conductor size, using NEC 310.16 ampacity and voltage-drop math. Unlike preset calculators that lock you into a specific service size (100A, 200A, etc.), this tool accepts any amp value, so it's equally useful for sizing a 15A outlet circuit, a 60A subpanel feed, a 150A commercial tap, or a 300A tenant-space service. It's the general-purpose wire sizer every electrician keeps a reference card for.
The underlying math is two-step: first, find the minimum AWG that carries the load per NEC Table 310.16 at your selected insulation column (60°C for older NM-B, 75°C for modern terminations, 90°C for derated or free-air runs). Second, run the voltage-drop formula V = (2 × K × L × I) ÷ CM to check whether that AWG actually delivers the load at acceptable voltage over your run length. If drop exceeds 3% on a branch circuit or 5% on a combined feeder + branch, the calculator upsizes to the next AWG until drop is under limit.
Inputs: amp rating, circuit voltage (120V, 240V, or 480V), run length one-way, conductor material (copper or aluminum), and insulation temperature rating. Output: required AWG, voltage drop %, ampacity margin, and whether the size is ampacity-limited or drop-limited.
Typical use cases: sizing a 20A kitchen small-appliance branch (12 AWG copper), a 60A subpanel feeder to a garage (6 AWG copper, short run), a 200A main service (typically 2/0 copper or 4/0 aluminum), or a long outbuilding feeder where the default wire size fails the drop check and needs an upsize. Equally useful for electricians, estimators, and homeowners scoping a project before pulling permits.
"How the Amp to Wire Size Calculator Works
Amp to AWG Formula
Same underlying formula as all wire sizing:
AWG size is the smallest wire where:
- NEC 310.16 ampacity ≥ load amps × safety factor
- Circular mils ≥ (2 × K × L × I) ÷ max voltage drop
Where K = 12.9 for copper, 21.2 for aluminum. For branch circuits target 3% voltage drop. For feeders 5% combined.
Example: 50 Amps to Wire Size
50A at 240V, 100 ft run, copper, 3% max drop:
- Ampacity check: 8 AWG = 50A ampacity → OK at 75°C THWN
- Voltage drop check: min cmils = (2 × 12.9 × 100 × 50) ÷ 7.2 = 17,917 cmils
- 8 AWG = 16,510 cmils → FAILS voltage drop
- Upsize to 6 AWG = 26,240 cmils → passes both
A 50A circuit uses 8 AWG for short runs, 6 AWG once you cross ~80-100 ft.
Common use cases
Amp-to-AWG Quick Reference (Copper, 75°C)
| Amps | Short Run AWG | Long Run (100+ ft) AWG |
|---|---|---|
| 15 | 14 | 12 |
| 20 | 12 | 10 |
| 30 | 10 | 8 |
| 40 | 8 | 6 |
| 50 | 8 | 6 |
| 60 | 6 | 4 |
| 100 | 3 | 2 |
| 125 | 1 | 1/0 |
| 150 | 1/0 | 2/0 |
| 200 | 3/0 | 4/0 |
Key Takeaways
The biggest advantage of a universal amp-to-wire calculator is that it forces the drop check on every circuit, not just the obvious ones. A 20A receptacle circuit 150 feet from the panel — common in a detached shop or outbuilding — needs 10 AWG instead of the \"code minimum\" 12 AWG. A 60A subpanel feed that looks fine at 6 AWG on paper might need 4 AWG over a 200-foot underground run.
Always pair the wire sizing with the right overcurrent protection (the breaker ampacity matches the wire, not the load), the right conduit fill (per NEC Chapter 9, Table 1), and the right ground (NEC 250.122 for equipment grounds, 250.66 for service grounds). This calculator handles the conductor math; code compliance still needs a licensed electrician and a permit for any new circuit or service work.
"Amp to Wire Size FAQs
What size wire for 30 amps?
What size wire for 50 amps?
What size wire for 100 amps?
What size wire for 200 amps?
What size wire for 15 amps?
What size wire for 20 amps?
What size wire for 40 amps?
What size wire for 60 amps?
Can I use 12 AWG for 30 amps?
Do I need bigger wire for aluminum?
Author Spotlight
The ToolsACE Team
Our specialized research and development team at ToolsACE brings together decades of collective experience in financial engineering, data analytics, and high-performance software development.
Disclaimer
Educational reference. Always verify with a licensed electrician.