Electrical
Electrical Wire Size Calculator
Review a preliminary conductor gauge alongside the gauge indicated by this tool's fixed voltage-drop comparison.
Result
A planning estimate, not a code calculation. Conductor sizing, overcurrent protection and load calculations are governed by the NEC as adopted and amended where you are, and by the listing of the equipment involved. Have the design confirmed by a licensed electrician and inspected. Ampacities here are the 75 degree copper and aluminium columns, before any derating for ambient temperature or for more than three current-carrying conductors in a raceway.
Get a Free Business AuditWhat moves the number
- The load is adjusted by the selected duration assumption.
- Copper and aluminium use different lookup values.
- The one-way route and system voltage determine the separate drop result.
Where this one goes wrong
The displayed Wire size is the table-based selection, while Size after voltage drop is a separate output. Do not read the first as a complete recommendation. Neither incorporates every installation adjustment or checks all possible protection arrangements.
Questions
About this calculator
Why are two gauges displayed?
One starts with the simplified current table. The other explores the run-length constraint, which can require a larger conductor even where the first gauge carries the current on paper.
Does the voltage selector change the circuit model?
It changes the voltage used in the percentage calculation. Selecting a commercial voltage does not turn the fixed circuit formula into a complete three-phase design.
What remains before specifying a conductor?
Verify terminations, cable type, derating and protection under the applicable code and equipment data. This is a planning check, not a substitute for that design.
The formula
design amps = load x 1.25 if continuous; voltage drop = 2 x K x amps x distance / circular mils
Put this calculator on your site
Free to embed. Paste this where you want it to appear. It stays up to date automatically because it loads from BDEVY.
Please keep the attribution line. It is the only thing we ask in return.
How to use this calculator
- Load (amps). Enter your own figure; the page starts at 30.
- Conductor. Enter your own figure; the page starts at Copper.
- Load type. Enter your own figure; the page starts at Normal load.
- One-way run length (ft). Enter your own figure; the page starts at 60.
- Voltage. Enter your own figure; the page starts at 240 V.
The result updates as you type, so you can try a figure, see what it does to wire size, and change it back. Nothing you enter is sent anywhere or saved.
A worked example
These are the figures the calculator opens with. Every number in the results column below is produced by the same calculation the page runs, so you can follow it through before putting your own figures in.
What goes in
| Input | Value |
|---|---|
| Load (amps) | 30 |
| Conductor | Copper |
| Load type | Normal load |
| One-way run length (ft) | 60 |
| Voltage | 240 V |
What comes out
| Result | Value |
|---|---|
| Wire size main result | 10 |
| Amps the wire must carry | 30 |
| Voltage drop at that size | 1.86% |
| Size after voltage drop | 10 |
For 30 amps you need 10 AWG. Over 60 feet that drops 1.86%, so on voltage drop alone you would run 10 AWG.
How sensitive the answer is
Holding everything else steady and changing only load (amps), this is what happens to wire size. It is worth knowing which of your inputs the answer actually hinges on, and which barely move it.
| Load (amps) | Wire size |
|---|---|
| 15 | 14 |
| 23 | 10 |
| 30 example above | 10 |
| 45 | 8 |
| 60 | 6 |
Every other input is held at the example value while this one changes, which is not how a real job behaves. Treat it as a guide to which number matters most, not as five separate quotes.
What each figure means
- Load (amps)
- A number, between 0 and 400, starting at 30.
- Conductor
- Choose from Copper, Aluminium.
- Load type
- Choose from Normal load, Continuous, 3 hours or more.
- One-way run length (ft)
- A number, between 0 and 2000, starting at 60.
- Voltage
- Choose from 120 V, 240 V, 208 V, 480 V.
What the results tell you
| Result | What it is |
|---|---|
| Wire size | The headline result. A category or planning selection, rather than a measured quantity. |
| Amps the wire must carry | A number. |
| Voltage drop at that size | A percentage. |
| Size after voltage drop | A category or planning selection, rather than a measured quantity. |
Before you rely on this number
Conductor sizing, voltage drop and load figures are governed by code, and the code takes precedence over any calculator. Ambient temperature, conduit fill, continuous load factors and the specific installation all change the answer. Treat this as a first pass, not a design.
Keep going
Related calculators
Electrical Breaker Size Calculator
Explore a preliminary breaker lookup from an entered current or a simple watts-to-current conversion.
Open calculatorElectrical Voltage Drop Calculator
Estimate voltage loss on a fixed conductor and inspect the longest run indicated by the tool's comparison threshold.
Open calculatorWire Ampacity Calculator
Inspect how ambient temperature and conductor grouping reduce a simplified table ampacity before a full installation review.
Open calculatorEstimating is the easy part
The jobs you never hear about cost more than the ones you mis-measure. BDEVY builds the marketing, systems and automation that bring them in.