Wire Gauge (AWG) Current Capacity Calculator

Wire gauge (AWG) current capacity calculator for safe amp estimates

This Wire Gauge (AWG) Current Capacity Calculator estimates how many amps a wire can carry safely for typical building and equipment wiring decisions. The most common real-world use case is simple: you know the wire gauge you plan to use (or what is already installed), and you want a defensible estimate of the maximum current before overheating becomes a risk. This is commonly called ampacity.

The calculator is intentionally locked to one decision: estimating a practical, code-style ampacity for a single conductor size, using a standard base table and straightforward adjustment factors. It is not a voltage drop calculator, not a motor starting calculator, and not a full electrical design tool. If your primary concern is long cable runs and voltage loss, you need a different tool. If your concern is inrush current, protective device curves, or specialty installations, this page is not trying to solve those cases.

To use it, select the AWG size and the conductor material. Copper is the default because it is the most common reference point. Then, optionally refine the estimate with the insulation temperature rating, ambient temperature, and the number of current-carrying conductors grouped together. The output gives you the adjusted ampacity estimate, a recommended continuous-load current (a conservative “do not run at the limit all day” number), and a suggested standard breaker size that does not exceed the estimated ampacity.

Assumptions and how to use this calculator

• Base ampacity values are table-style estimates for typical building wire sizes, intended for common 60°C, 75°C, and 90°C insulation ratings at a 30°C ambient reference.
• Ambient temperature adjustment is applied as a simple correction factor around 30°C. If you leave ambient blank, the calculator assumes 30°C.
• Conductor bundling adjustment is applied using a simplified conductor-count factor. If you leave conductor count blank, the calculator assumes 3 current-carrying conductors.
• The result is an estimate for steady-state current. It does not model short-duration inrush, motor starting, or rapid cycling loads.
• The recommended “continuous load” figure is a conservative 80% of the adjusted ampacity to reflect practical heat margin. Your local code and installation details can be stricter.

Common questions

Why do copper and aluminum give different current capacities?

Aluminum typically has higher electrical resistance than copper for the same cross-sectional size, so it tends to run hotter at the same current. That is why standard ampacity tables usually show lower allowable current for aluminum than for copper of the same AWG size.

What should I enter for insulation temperature rating if I do not know it?

If you are unsure, 75°C is a practical default for many common wiring types, but the safest conservative choice is 60°C. If you need a cautious estimate, choose 60°C. If you know the marking on the cable jacket, use that rating.

Does this replace electrical code or a qualified electrician?

No. This is an estimating tool for typical scenarios. Real allowable current depends on installation method, termination temperature limits, local regulations, and the specific cable and environment. Use this to sanity-check and to plan, then verify against applicable code and professional guidance for any high-risk or regulated work.

Why does the result change when I increase the number of conductors?

When multiple current-carrying conductors are bundled together, they heat each other and the assembly sheds heat less effectively. Standard practice applies a derating factor once you go above a small number of conductors. That is why the calculator reduces allowable current as conductor count increases.

Should I use the “ampacity” number or the “continuous load” number?

If the load will run for long periods (space heating, continuous equipment, always-on loads), the continuous-load figure is the safer planning number because it builds in heat margin. For short or intermittent loads, the ampacity estimate can be a reasonable upper bound, but you still should not treat it as a target to run at constantly.