Amp to Wire Size Calculator
Convert amps into a practical wire gauge (AWG) using common reference ampacity tables.
Your Wire Size Result
- Enter amps — Type the current you want the wire to carry.
- Pick copper/aluminum — Material affects ampacity and resistance.
- Choose 60/75/90°C — These are common planning columns in reference tables.
- Read the gauge — The calculator picks the smallest gauge meeting the input amps.
- Use voltage drop separately — Long runs may need upsizing even if ampacity is sufficient.
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. Breaker sizes come in standard steps and some loads are treated as continuous, so the “right” breaker and wire can be one size higher depending on the scenario.
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 this with 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 for quick planning: you have amps and want a starting gauge in seconds.
Use Wire Size when you want more context (material choice, temperature column, and related sizing checks like voltage drop).
If you are building a full circuit plan, a common flow is: Watts/Amps/Volts → Electrical Load → Breaker Size → Wire Size → Voltage Drop.
Typical Amps for Common Devices (Quick Planning)
| Device | Watts | Voltage | Approx. amps |
|---|---|---|---|
| Space heater | 1500 W | 120 V | 12.5 A |
| Microwave | 1200 W | 120 V | 10.0 A |
| Electric kettle | 1500 W | 120 V | 12.5 A |
| Small water heater | 3500 W | 240 V | 14.6 A |
| EV charger (Level 2) | 7200 W | 240 V | 30.0 A |
These are rough conversions (PF assumed 1.0). Use the Electrical Load Calculator when summing many items.
Fast Lookups People Commonly Need
| Amps | Often Planned Copper Gauge | Often Planned Aluminum Gauge |
|---|---|---|
| 15 | 14 AWG | 12 AWG |
| 20 | 12 AWG | 10 AWG |
| 30 | 10 AWG | 8 AWG |
| 40 | 8 AWG | 6 AWG |
| 50 | 6 AWG | 4 AWG |
Planning reference only. Verify for your installation conditions.
Starter Gauge Logic (Amp → AWG)
This tool gives a fast starting gauge from your amps. It is intentionally conservative and meant for early planning.
Temperature columns = 60°C/75°C/90°C tables can differ. Use the column that matches your project assumptions
Sanity checks = Confirm breaker size and voltage drop before you buy materials
For a full circuit plan (multiple loads, phases, long distance), use Electrical Load and Voltage Drop calculators too.
Related Calculators
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.
Why does the breaker result not equal my amps?
Breakers are sized at 125% of continuous load per NEC requirements, so a 16A continuous load requires a 20A breaker. The next standard breaker size up is always selected — breakers come in 15, 20, 30, 40, 50, 60A and larger increments.
What wire size do I need for a 30 amp circuit?
A 30A circuit requires 10 AWG copper wire (or 8 AWG aluminum). This is common for dryers, EV chargers, and water heaters. Always verify with local code — some jurisdictions require larger wire for specific applications or longer runs where voltage drop becomes significant.
What wire size do I need for a 20 amp circuit?
A 20A circuit requires 12 AWG copper wire minimum. This is the most common circuit size for kitchen outlets, bathroom outlets, and general workshop circuits. Many electricians use 12 AWG for all outlet circuits even when 14 AWG would technically be allowed, for future flexibility.
Does insulation temperature rating change the wire size?
Yes. Ampacity tables are typically shown for different temperature ratings (often 60°C, 75°C, 90°C). The same AWG can have different allowable amps depending on the column you use, terminations, and installation conditions.