When makers, DIYers, and trade students search for an amp conversion chart, they are typically looking for one of two things: how to convert watts and volts into amps, or how to convert American Wire Gauge (AWG) sizes into maximum safe ampacity. This guide provides both, starting with the definitive NEC Table 310.16 wire-to-amp chart you need for sizing branch circuits and feeders.
The quick answer for standard residential copper (NM-B / Romex): 14 AWG is rated for 15 amps, 12 AWG is rated for 20 amps, 10 AWG is rated for 30 amps, and 8 AWG is rated for 40 amps. However, relying on a simple list without understanding temperature columns and derating factors is how wires melt inside walls. Below is the complete reference data you need to size conductors safely and legally.
The NEC Wire Size to Amp Conversion Chart (Table 310.16)
The following table is derived from NFPA 70: National Electrical Code (NEC) Table 310.16 (formerly 310.15(B)(16)). It lists the allowable ampacities for insulated copper conductors rated up to 2000 volts.
How to read this table: The rows represent the wire gauge (AWG or kcmil). The columns represent the temperature rating of the wire's insulation (60°C, 75°C, and 90°C). Bookmark the bolded rows below, as they represent the most queried values for standard residential branch circuits.
| Copper Wire Size (AWG/kcmil) | 60°C (140°F) Column | 75°C (167°F) Column | 90°C (194°F) Column |
|---|---|---|---|
| 14 AWG (Most queried) | 15 A | 20 A | 25 A |
| 12 AWG (Most queried) | 20 A | 25 A | 30 A |
| 10 AWG (Most queried) | 30 A | 35 A | 40 A |
| 8 AWG | 40 A | 50 A | 55 A |
| 6 AWG | 55 A | 65 A | 75 A |
| 4 AWG | 70 A | 85 A | 95 A |
| 3 AWG | 85 A | 100 A | 115 A |
| 2 AWG | 95 A | 115 A | 130 A |
| 1 AWG | 110 A | 130 A | 145 A |
| 1/0 AWG | 125 A | 150 A | 170 A |
| 2/0 AWG | 145 A | 175 A | 195 A |
| 3/0 AWG | 165 A | 200 A | 225 A |
| 4/0 AWG | 195 A | 230 A | 260 A |
Source Standard: Data sourced from NEC Article 310.16. Always verify against your local Authority Having Jurisdiction (AHJ), as local amendments may supersede national code baselines. For further code interpretations, consult EC&M National Electrical Code Resources.
Which Column Applies to Your Installation?
The most common mistake DIYers make with an amp conversion chart is looking at the 90°C column because modern THHN/THWN-2 wire is rated for 90°C, and then assuming they can push 40 amps through a 10 AWG wire. This is incorrect and a fire hazard.
You must use the lowest temperature rating of any component in the circuit. This is known as the termination temperature limit.
- The 60°C Column: Use this for almost all residential branch circuits rated 100 amps or less. Standard duplex receptacles, light switches, and standard miniature circuit breakers are typically only tested and rated for 60°C terminations. Even if your wire is 90°C THHN, the breaker lug is the weak link. Therefore, 12 AWG is capped at 20A, and 10 AWG is capped at 30A.
- The 75°C Column: Use this for residential feeders, subpanels, and main breakers rated 100 amps and above. Modern load centers and large breakers generally feature 75°C rated lugs. This is why a 3 AWG copper feeder can safely be placed on a 100A main breaker.
- The 90°C Column: You rarely use this column to determine your final breaker size. Its primary legal use in the NEC is as the starting baseline for calculating derating factors (explained below) before you apply the termination temperature cap.
How Derating Modifies Your Base Ampacity
The amp conversion chart above assumes two things: an ambient temperature of 30°C (86°F), and no more than three current-carrying conductors bundled together in a single raceway or cable. When you violate either assumption, the wire cannot dissipate heat as efficiently, and you must reduce (derate) the allowable ampacity.
Bundling Derating (NEC 310.15(C)(1))
When you pull multiple circuits through a single conduit, the heat from adjacent wires compounds. You must apply a derating multiplier to the 90°C column value, and then compare that result to your termination limit, using whichever is lower.
- 4 to 6 conductors: Multiply base ampacity by 80%
- 7 to 9 conductors: Multiply base ampacity by 70%
- 10 to 20 conductors: Multiply base ampacity by 50%
Worked Example: You are pulling four 12 AWG THHN circuits (8 current-carrying conductors total) through a single PVC conduit to a detached garage.
1. Base 90°C ampacity for 12 AWG = 30A.
2. Apply 80% derating for 4-6 conductors per circuit (wait, 8 total conductors means we use the 7-9 conductor row: 70%).
3. 30A × 0.70 = 21A.
4. Check termination limit: Standard 20A breaker lugs are 60°C rated, which caps 12 AWG at 20A.
5. Final allowable ampacity is 20A. The 21A derated value is higher than the 20A termination limit, so the 20A breaker is perfectly legal and safe. If you had pulled 10 circuits (requiring 50% derating), 30A × 0.50 = 15A, and you would be forced to upsize to 10 AWG wire.
Ambient Temperature Derating
If your conduit runs across an attic in a hot climate where ambient temperatures reach 110°F (43°C), you must multiply the 90°C base ampacity by 0.82 (per NEC Table 310.15(B)(1)). A 10 AWG wire (40A base at 90°C) derates to 32.8A. Because 32.8A is higher than the 60°C termination limit of 30A, you can still use a 30A breaker. But if the attic hits 130°F, the multiplier drops to 0.71 (40A × 0.71 = 28.4A), forcing you to upsize to 8 AWG to maintain a 30A circuit.
What This Chart Cannot Tell You (And Power Formulas)
An ampacity chart only tells you the threshold at which the wire's insulation will degrade or the copper will melt. It does not account for voltage drop.
If you run 14 AWG wire at its maximum 15A capacity for 60 feet on a 120V circuit, the wire will not catch fire. However, the resistance of the copper will cause a voltage drop of roughly 4.7 volts (nearly 4%). The NEC recommends a maximum 3% voltage drop for branch circuits to ensure motors don't overheat and lights don't dim. For long runs, you must upsize the wire purely for voltage drop management, regardless of what the ampacity chart permits.
Watts to Amps Conversion Table
If your search for an amp conversion chart was actually about figuring out how many amps a specific appliance draws, you need the power formula: Amps = Watts ÷ Volts (for purely resistive DC or AC loads with a power factor of 1.0). For inductive loads like motors, you must also divide by the Power Factor (PF), typically 0.8 to 0.9.
| Appliance Wattage | Amps Drawn @ 120V (US Standard) | Amps Drawn @ 240V (EU/UK Standard or US Heavy Appliance) |
|---|---|---|
| 500W (Work light / small tool) | 4.17 A | 2.08 A |
| 1500W (Space heater / microwave) | 12.50 A | 6.25 A |
| 1800W (Hair dryer / toaster oven) | 15.00 A (Maxes out a 15A circuit) | 7.50 A |
| 3000W (Baseboard heater) | 25.00 A | 12.50 A |
| 4500W (Electric water heater) | 37.50 A | 18.75 A |
| 7200W (EV Charger / Electric range) | 60.00 A | 30.00 A |
When sizing a breaker for a continuous load (anything expected to run for 3 hours or more, like an EV charger or space heater), the NEC requires you to multiply the calculated amp draw by 1.25. A 1500W space heater on a 120V circuit draws 12.5A. Multiplied by 1.25, the required circuit capacity is 15.62A. This is why a 15A breaker will eventually trip on a continuous 1500W load; you must dedicate a 20A circuit (12 AWG wire) to safely run it continuously.
