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Amp to Wire Size Calculator

By · Updated Aug 2026

A fast ampacity-to-AWG lookup for early planning. Distance, voltage drop, and installation-specific adjustment are intentionally left to the full Wire Size tool.

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How to Use

  1. Enter amps - Type the current you want the conductor to carry.
  2. Pick material - Copper and aluminum use different ampacity references.
  3. Pick the basis - Choose the final ampacity basis you are screening. The 75°C option is only appropriate where the applicable conductor/equipment termination conditions permit it; NM-B does not exceed its 60°C ampacity basis.
  4. Read the quick gauge - The tool returns the first configured AWG whose usable planning ampacity meets the entered current.
  5. Move to full sizing when needed - If distance, continuous-load treatment, or correction/adjustment factors matter, use the Wire Size Calculator instead of treating this quick lookup as a final design.
Quick answer

Enter the current and choose the conductor material plus ampacity basis. The tool returns the first configured gauge whose usable planning ampacity meets the input, including the small-conductor protection caps in its data model. It intentionally does not guess distance, correction/adjustment factors, terminations, or load-specific rules.

How the Quick Lookup Chooses a Gauge

1. Enter currentamps2. Choose materialcopper or aluminum4. Read the gaugefirst passing AWG3. Choose basis60°C or 75°CDistance and installation adjustments belong in the full Wire Size Calculator.
The quick tool is intentionally narrow: current plus material plus ampacity basis. It does not guess installation conditions that belong in full conductor sizing.

Amps to Wire Size: What This Tool Does

This page is a quick ampacity-to-gauge lookup. Enter amps and select copper or aluminum, and the calculator returns a smallest wire size that meets the input using a simplified planning table.

It's designed for fast comparisons, not final design. Load-specific treatment, ambient conditions, conductor grouping, terminations, and voltage drop can require a different final size.

Example: a 30A circuit may map to a common copper gauge, but if the run is long the voltage drop may drive you to upsize. Use the Voltage Drop Calculator when distance is significant.

Amp-to-Wire Size vs Wire Size: What's the Difference?

Both tools point you to a practical AWG range, but they start from different inputs and are used at different stages.

Use Amp-to-Wire Size when you already know the current and only need a fast starting gauge.

Use Wire Size when you want the full workflow: continuous-load planning factor, material, ampacity basis, automatic ambient-temperature and conductor-count adjustment, termination limits, and optional voltage-drop sizing.

If you are building a full circuit plan, use this page only as a quick lookup and move to Wire Size for the actual sizing workflow.

Typical Amps for Common Devices (Quick Planning)

DeviceWattsVoltageApprox. amps
Space heater1500 W120 V12.5 A
Microwave1200 W120 V10.0 A
Electric kettle1500 W120 V12.5 A
Small water heater3500 W240 V14.6 A
EV charger (Level 2)7200 W240 V30.0 A

These are rough conversions (PF assumed 1.0). Use the Electrical Load Calculator when summing many items.

Fast Lookups (Copper & Aluminum, Conduit 75°C)

AmpsCopper (THHN, conduit)Aluminum (THHN, conduit)
15 A14 AWG12 AWG
20 A12 AWG10 AWG
30 A10 AWG8 AWG
40 A8 AWG8 AWG
50 A8 AWG6 AWG

Copper in conduit at the 75°C column, matching this calculator default. For NM-B cable (Romex) size one column cooler at 60°C: a 50 A circuit becomes 6 AWG copper. Remember NEC 240.4(D) caps 14/12/10 AWG copper at 15/20/30 A breakers.

Starter Gauge Logic (Amp to AWG)

This tool gives a fast starting gauge from your amps. It is intentionally narrow and meant for early planning.

Starter gauge = Map your input amps to the first gauge that meets/clears it in the selected column
Wiring method = NM-B uses the 60°C maximum in this quick model. The THHN/THWN-2 option uses the 75°C ampacity basis only where permitted.
Sanity checks = Confirm installation-specific adjustment, conductor terminations, load rules, and voltage drop before buying materials

For distance-aware sizing, use the Wire Size Calculator. Use Voltage Drop when you want to evaluate a conductor size you already chose.

Code Notes & Sources

  • Ampacities follow NEC Table 310.16 for copper and aluminum. The 240.4(D) small-conductor rule then caps overcurrent protection at 15, 20, and 30 amps for 14, 12, and 10 AWG copper regardless of the table value, and this tool enforces it.NFPA 70 (NEC) Table 310.16 and 240.4(D)
  • NM-B cable ampacity does not exceed the 60°C conductor basis; its 90°C rating may be used for adjustment/correction calculations only when the final calculated ampacity remains within the 60°C limit.NFPA NEC development record - 334.80 ampacity

Next Steps

A starting gauge is not the whole circuit. Confirm the rest:

  1. Check long runsDistance can force a larger wire than ampacity alone - verify the drop.
  2. Check raceway fillIf these conductors share a raceway, verify the bundle and conduit size separately.
  3. Full wire sizingAdd continuous-load treatment, ambient and conductor-count adjustment, termination limits, and optional distance/voltage-drop sizing.

Related Calculators

Electrical Load CalculatorFind the amps first.Cable Tray Fill CalculatorTray capacity for grouped cable runs.Ohm's Law CalculatorVolts, amps, and resistance.Watts Amps Volts CalculatorConvert watts to amps.

Amps drive both wire gauge and breaker selection. Browse the electrical calculator collection.

FAQ

Do I always pick the smallest wire that matches amps?
Not always. Distance (voltage drop), ambient temperature, bundling, and terminations can require a larger conductor.
Does this calculator include voltage drop or derating?
No. This is deliberately the quick lookup. It uses the selected ampacity basis and small-conductor planning caps, but it does not guess distance, ambient-temperature correction, conductor-group adjustment, termination limits, or load-specific rules. Use the Wire Size Calculator when those inputs matter.
What does this quick tool return for a 30 amp copper input?
Under the quick lookup's copper ampacity baseline and small-conductor planning cap, a 30 A input maps to 10 AWG copper. That is not a universal installation prescription: load type, wiring method, terminations, adjustment factors, voltage drop, equipment instructions, and locally adopted code can change the final design.
What does this quick tool return for a 20 amp copper input?
Under the quick lookup's copper baseline, a 20 A input maps to 12 AWG copper because the small-conductor planning cap prevents 14 AWG copper from being treated above 15 A. Verify the actual circuit, conductor type, terminations, equipment requirements, and locally adopted code before installation.
Does insulation temperature rating change the wire size?
Yes, indirectly. NM-B cable does not exceed the 60°C ampacity basis. A 75°C ampacity basis may be used only where the conductor/equipment termination conditions permit it, so the same AWG can have a different usable ampacity depending on the actual installation. If you are pulling several conductors together, check raceway capacity with the Conduit Fill Calculator.
Updated Aug 2026 · See our Methodology
Quick planning lookup only. It does not include voltage drop, continuous-load treatment, ambient-temperature correction, current-carrying-conductor adjustment, termination limitations, equipment instructions, or every locally adopted code condition. Use the full Wire Size Calculator when those factors matter.