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Wire Size Calculator

Find the minimum conductor size for a load based on ampacity, temperature, bundling and distance.

Load
A
V
Conductor
Material

NEC 110.14(C) limits you to the lowest-rated termination in the circuit.

Neutrals on a balanced multiwire circuit and grounds do not count.

Installation
Phase
ft

Measure the actual routed distance, not the straight line.

Minimum conductor size

8 AWGcopper

Sized by corrected ampacity; voltage drop is within your limit.
Design currentLoad as entered
50.0 A
Overcurrent deviceNext standard size, NEC 240.6(A)
50 A
Voltage drop at this size5.8 V lost over 75 ft
2.43%
Derating appliedAmbient 100% × bundling 100%
100%

Ampacity governs this size

The conductor is sized by corrected ampacity, and voltage drop over 75 ft is within your 3% limit at 2.43%.
Candidate sizes under these conditions
SizeTable ampacityAfter deratingVoltage dropStatus
14 AWG20 A20.0 A9.81%Ampacity short
12 AWG25 A25.0 A6.19%Ampacity short
10 AWG35 A35.0 A3.88%Ampacity short
8 AWG50 A50.0 A2.43%Compliant
6 AWG65 A65.0 A1.53%Compliant
4 AWG85 A85.0 A0.96%Compliant
3 AWG100 A100.0 A0.77%Compliant
2 AWG115 A115.0 A0.61%Compliant
1 AWG130 A130.0 A0.48%Compliant
1/0 AWG150 A150.0 A0.38%Compliant
2/0 AWG175 A175.0 A0.30%Compliant
3/0 AWG200 A200.0 A0.24%Compliant
4/0 AWG230 A230.0 A0.19%Compliant
250 AWG255 A255.0 A0.16%Compliant

NEC Table 310.16 ampacity quick reference

Not more than three current-carrying conductors in a raceway, 30°C ambient. Termination and derating may require a larger size — use the calculator above for your run.

Copper and aluminum ampacity by wire size at 60°C and 75°C terminations
AWG/kcmilCu 60°CCu 75°CAl 60°CAl 75°C
1415 A20 A——
1220 A25 A15 A20 A
1030 A35 A25 A30 A
840 A50 A35 A40 A
655 A65 A40 A50 A
470 A85 A55 A65 A
385 A100 A65 A75 A
295 A115 A75 A90 A
1110 A130 A85 A100 A
1/0125 A150 A100 A120 A
2/0145 A175 A115 A135 A
3/0165 A200 A130 A155 A
4/0195 A230 A150 A180 A

Source: NEC Table 310.16 (copper and aluminum). Termination limits per NEC 110.14(C) may require sizing from the 60°C column.

Quick answer

For a typical 50-amp branch circuit with 60°C terminations, 6 AWG copper is the common minimum for short runs; a 100-amp subpanel feeder usually needs 3 AWG copper or 1 AWG aluminum for ampacity, and longer runs may require a larger size for voltage drop. Conductor size must satisfy table ampacity after temperature and bundling adjustments, termination limits (often 60°C on breakers 100A and under), and a voltage-drop check — the largest size required wins. Use the calculator below with your load amps, length, and installation details; verify against locally adopted NEC and equipment listings before installing.

What this assumes

  • Ampacity values come from NEC Table 310.16 for not more than three current-carrying conductors in a raceway, at 30°C ambient.
  • Temperature correction uses NEC Table 310.15(B)(1); bundling adjustment uses Table 310.15(C)(1).
  • Termination temperature is limited to 60°C for circuits of 100A or less unless equipment is listed for 75°C, per NEC 110.14(C).

Important

This is a planning aid, not a design. Conductor sizing depends on the installation method, the specific equipment listing and locally adopted amendments. A licensed electrician must verify any installed circuit.

Understanding the result

Three constraints, not one

A conductor has to satisfy three separate limits at once: the table ampacity after correction and adjustment, the temperature rating of the terminations at both ends, and an acceptable voltage drop over the run. The governing size is whichever of the three is largest — which is why a short 50A run and a 200-foot 50A run need different wire.

Why terminations often decide the answer

NEC 110.14(C) limits you to the lowest temperature rating in the circuit. Most breakers and equipment 100A and under are listed for 60°C terminations, so even though a 90°C conductor has higher table ampacity, you must size from the 60°C column. The 90°C column is used only as the starting point for derating.

Copper versus aluminum

Aluminum carries roughly 61% of copper's conductivity, so an aluminum conductor is typically two AWG sizes larger for the same ampacity. It costs substantially less on large feeders, which is why service entrance and feeder conductors are commonly aluminum while branch circuits are copper.

Continuous loads change breaker sizing

A load running 3 hours or more is continuous and limited to 80% of breaker rating. A 50-amp continuous load needs a 70-amp breaker and wire sized for 70 amps — not 50. EV chargers, water heaters, and heat strips are common continuous loads that push wire size beyond what the nameplate amperage suggests.

Common questions

What size wire do I need for a 50 amp circuit?
For a typical 50A branch circuit with 60°C terminations, 6 AWG copper is the common answer for short runs. Longer runs, high ambient temperature, or more than three current-carrying conductors in the raceway can push that to 4 AWG or larger.
Does conduit fill change the wire size?
Yes. Once you have more than three current-carrying conductors in a raceway, NEC Table 310.15(C)(1) reduces allowable ampacity — 80% for four to six conductors, 70% for seven to nine, and lower beyond that.
What size wire for a 100 amp sub panel?
A 100-amp sub panel feeder needs 3 AWG copper or 1 AWG aluminum minimum for ampacity at 75°C. For a 100-foot run, voltage drop may require 1/0 copper or 2/0 aluminum. Include a 6 AWG copper or 4 AWG aluminum ground per NEC 250.122.
Can I use 12 gauge wire on a 20 amp circuit?
Yes. 12 AWG copper is rated for 20 amps at 60°C and 25 amps at 75°C. A 20-amp breaker on 12 AWG is the standard combination. You cannot use 14 AWG on a 20-amp circuit — 14 AWG is limited to 15 amps.
What size wire for a 200 amp service?
A 200-amp service entrance needs 2/0 copper or 4/0 aluminum minimum per NEC Table 310.16. For runs over 100 feet, voltage drop may require 3/0 copper or 250 kcmil aluminum. The ground electrode conductor is 4 AWG copper or 2 AWG aluminum.
What size wire for a 30 amp dryer?
A 30-amp dryer circuit needs 10 AWG copper with a 30-amp breaker. For runs over 75 feet, check voltage drop — a 1,500-watt heating element at 30 amps on 100 feet of 10 AWG drops about 5.9V (2.5% on 240V), which is acceptable.
What size wire for a 40 amp stove?
A 40-amp range circuit needs 8 AWG copper with a 40-amp breaker. Most modern ranges on 240V draw 30 to 40 amps on the heating elements. A 50-amp circuit with 6 AWG is common for ranges with high-wattage ovens.
What size wire for a 60 amp hot tub?
A 60-amp hot tub circuit needs 6 AWG copper with a 60-amp two-pole breaker. Hot tubs typically require GFCI protection. For runs over 100 feet, check voltage drop — 6 AWG on 100 feet at 50 amps drops about 6.2V (2.6% on 240V).
What size aluminum wire for 100 amps?
1 AWG aluminum is rated for 100 amps at 75°C. For a sub panel feeder, use 1 AWG or 1/0 aluminum depending on voltage drop. The ground for a 100-amp circuit is 4 AWG aluminum per NEC 250.122. Always apply anti-oxidant compound on aluminum terminations.
What size wire for a 15 amp circuit?
14 AWG copper is the standard for 15-amp circuits — lighting and general receptacles. Maximum load is 1,800 watts (15 × 120). For runs over 100 feet on a heavily loaded circuit, check voltage drop, but 14 AWG is adequate for most residential branch circuits.
What size wire for 150 feet at 50 amps?
At 50 amps over 150 feet, 6 AWG copper drops about 9.3V (3.9% on 240V) — borderline. Upsize to 4 AWG copper for 2.4% drop or 3 AWG for 1.9%. Ampacity is not the constraint here — voltage drop governs the size.

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