Wire Size Calculator
SAFETY DISCLAIMER: This calculator is for estimation and education only. It is NOT a substitute for a licensed electrician or the National Electrical Code as adopted by your local authority having jurisdiction (AHJ). Wire sizing depends on factors this tool may not capture — ambient temperature, number of conductors in raceway, conduit fill, termination ratings, derating factors, and local code amendments. Incorrect wire sizing can cause fire or electrocution. Always have your wiring designed, installed, and inspected by a licensed electrician and obtain a permit.

Wire Size Calculator

Find the correct AWG conductor size using NEC 2023 ampacity and voltage-drop calculations. Copper or aluminum • Single-phase or three-phase • Your inputs never leave your browser.

Inputs

Min AWG by Ampacity
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Min AWG for Voltage Drop
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Recommended AWG
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Actual Voltage Drop
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SAFETY REMINDER: This tool provides estimates only. Always verify wire sizing with a licensed electrician before installation. Obtain a permit. Incorrect wire sizing can cause fire or electrocution.

NEC 2023 Table 310.16 — 75°C Ampacity Reference

Allowable ampacities from NEC 2023 (NFPA 70) Table 310.16, 75°C column. Conditions: insulated conductors in raceway or cable, not more than 3 current-carrying conductors, 30°C (86°F) ambient. Values cross-verified against published references as of June 2026. Note: Per NEC 240.4(D), 14, 12, and 10 AWG copper are limited to 15 A, 20 A, and 30 A overcurrent protection (12 AWG and 10 AWG aluminum to 15 A and 25 A) regardless of the higher 75°C ampacity shown — this calculator applies those limits when recommending a size. The minimum branch-circuit conductor is 14 AWG copper / 12 AWG aluminum per NEC 310.3(B); many electricians and jurisdictions also avoid small aluminum for branch circuits, so verify with your AHJ.

AWG Size Copper 75°C (A) Aluminum 75°C (A) Circular Mils
14 AWG20—4,107
12 AWG25206,530
10 AWG353010,380
8 AWG504016,510
6 AWG655026,240
4 AWG856541,740
3 AWG1007552,620
2 AWG1159066,360
1 AWG13010083,690
1/0 AWG150120105,600
2/0 AWG175135133,100
3/0 AWG200155167,800
4/0 AWG230180211,600

Source: NEC 2023 (NFPA 70) Table 310.16. Circular-mil values from Engineering Toolbox AWG reference table, cross-checked against LearnMetrics AWG-to-Circular-Mils chart. Both verified June 2026. Data is re-expressed as a lookup table — not a verbatim reproduction of the NFPA 70 table. Always consult the official NEC edition adopted in your jurisdiction.

Frequently Asked Questions

What NEC table does this calculator use?

This calculator uses NEC 2023 (NFPA 70) Table 310.16, specifically the 75°C column for insulated conductors in raceway or cable with not more than three current-carrying conductors at 30°C (86°F) ambient. The 75°C column is the most commonly used column in practice because NEC 110.14(C) limits most terminations (breakers, lugs) to 75°C regardless of conductor insulation rating.

What is the "continuous load" toggle?

Per NEC 210.20(A) and 215.3, a continuous load (energized 3+ hours continuously) must be limited to 80% of the breaker/wire rating. Enabling this toggle applies the 125% inverse factor to your load amps before finding the minimum wire size — the same effect as the 80% rule.

What is voltage drop and why does 3% matter?

Voltage drop is the loss of voltage along a wire due to its resistance. At 3% drop on a 120V circuit, the device at the end sees 116.4V. The NEC recommends (but does not mandate) a maximum of 3% voltage drop on branch circuits (NEC 210.19(A) informational note) and 5% total from service to outlet. This calculator defaults to 3% for branch circuits.

Why does the calculator recommend the larger of two sizes?

Wire must satisfy two independent requirements: it must be large enough to carry the current safely (ampacity), and large enough to keep voltage drop within your target. Either constraint may be the binding one depending on run length. The recommended size is the larger of the two — the conservative, safe choice.

Can I use aluminum wire for branch circuits?

Aluminum is commonly used for service entrance conductors, feeders, and larger circuits, but NEC 310.3(B) and most AHJs restrict aluminum to conductors size 6 AWG and larger for most applications. Aluminum requires rated connectors and anti-oxidant compound. Always verify with your local AHJ and a licensed electrician before specifying aluminum.

Does this tool account for conductor derating?

No. This tool gives the base ampacity from NEC Table 310.16 under standard conditions (30°C ambient, ≤3 conductors in raceway). Real installations may require derating for high ambient temperature (NEC Table 310.15(B)(1)), bundled conductors (NEC 310.15(C)), or conduit fill. A licensed electrician must apply all applicable derating factors.

Is this tool free and do I need to sign up?

Yes — completely free, no account required. All calculations happen in your browser. Your inputs never leave your device.

Guides & Resources

Step-by-step articles covering NEC ampacity rules, voltage drop, conductor materials, and special-purpose circuits.