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Cable Size Calculator

Calculate the appropriate electrical cable size based on current, voltage, distance, and installation conditions.

Recommended size
Recommended size
4/0 AWG
Current capacity
230 A
Voltage drop
0.15%
Power loss
10.94 W
Max length for 3% drop
197,368.4 ft
First alternatives
14 AWG: 20A, 7.85%; 12 AWG: 25A, 4.95%; 10 AWG: 35A, 3.10%; 8 AWG: 50A, 1.94%

Simplified sizing table only; electrical designs must be checked against applicable code by a qualified professional.

A
ft

Results update as you type.

Cable Size Calculator

Estimate a practical electrical cable size from voltage system, voltage, current, cable length, conductor material, insulation type, installation method, and ambient temperature. The output includes recommended AWG size, current capacity, voltage drop, power loss, maximum length for a 3 percent drop, and first alternatives.

How to use this calculator

Select single phase or three phase, choose system voltage, then enter current in amps and cable length in feet. Pick copper or aluminum, insulation, installation method, and ambient temperature. The calculator derates ampacity for temperature and installation before testing voltage drop.

How it works

For single phase, voltage drop uses a round-trip factor of 2. For three phase, it uses square root of 3:

voltage drop percent=factor×current×resistance×length÷(1000×voltage)×100voltage\ drop\ percent = factor \times current \times resistance \times length \div (1000 \times voltage) \times 100

With 30 A, 240 V, 100 ft, copper, PVC, conduit, and 30 °C, the simplified table selects the first size that satisfies both adjusted current and voltage drop.

Safety notes

This tool is for early planning only. Real installations also depend on conductor count, conduit fill, terminal temperature ratings, breaker size, insulation listing, local code, and continuous-load rules. For project planning around walls or framing, the stud spacing calculator and square footage calculator may help measure the route.

Frequently asked questions

How does this calculator choose cable size?
It checks the simplified AWG table for ampacity after derating and a voltage drop of 3 percent or less.
Does cable length affect wire size?
Yes. Longer cable runs increase voltage drop, so a larger conductor may be recommended even when ampacity is adequate.
Can I compare copper and aluminum cable?
Yes. Select copper or aluminum and the calculator uses different ampacity and resistance values for each material.
Is this a code-approved electrical design?
No. It is a simplified estimator, and electrical work should be checked by a qualified professional against applicable code.

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Cable Size Calculator updated at