Electrical

Wire Ampacity Calculator

Inspect how ambient temperature and conductor grouping reduce a simplified table ampacity before a full installation review.

Result

Adjusted table ampacity 35.0 Amps, before terminal and protection limits

Table ampacity at 75 C 35 Amps

Temperature factor 1.0

Conductor count factor 1.0

10 AWG starts at 35 amps and derates to 35.0 amps at 30 C with 3 conductors in the raceway.

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. Ampacity is also limited by the temperature rating of the terminations at both ends, which for most residential equipment is 60 or 75 degrees regardless of what the conductor itself is rated for. Small conductors additionally have fixed overcurrent limits.

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What moves the number

Material and gauge select the starting table value.
The ambient selection changes the temperature multiplier.
The conductor-count input represents current-carrying conductors, not simply every item in the raceway.

Where this one goes wrong

Usable ampacity is a model output, not unconditional permission to protect the wire at that current. Terminal ratings, cable installation limits and small-conductor rules can control the final value even after these multipliers are applied.

Questions

About this calculator

Is conductor count the same as conduit fill?

No. Thermal adjustment and occupied raceway area answer different questions. Determine which conductors count under the applicable rules before entering the number.

Can I use the insulation temperature alone?

The connected equipment and installation method matter too. A high insulation rating does not automatically permit the same temperature basis at the terminals.

Does this replace the adopted ampacity tables?

It is a planning illustration of two adjustments. Use the locally applicable code and equipment documentation for a complete conductor and protection assessment.

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The formula

usable ampacity = table value x temperature factor x conductor-count factor

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How to use this calculator

Wire size. Enter your own figure; the page starts at 10 AWG.
Conductor. Enter your own figure; the page starts at Copper.
Ambient temperature. Enter your own figure; the page starts at Up to 30 C / 86 F (factor 1.00).
Current-carrying conductors in the raceway. Enter your own figure; the page starts at 3.

The result updates as you type, so you can try a figure, see what it does to adjusted table ampacity, 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
Wire size	10 AWG
Conductor	Copper
Ambient temperature	Up to 30 C / 86 F (factor 1.00)
Current-carrying conductors in the raceway	3

What comes out

Result	Value
Adjusted table ampacity main result	35.0
Table ampacity at 75 C	35
Temperature factor	1.0
Conductor count factor	1.0

10 AWG starts at 35 amps and derates to 35.0 amps at 30 C with 3 conductors in the raceway.

How sensitive the answer is

Holding everything else steady and changing only current-carrying conductors in the raceway, this is what happens to adjusted table ampacity. It is worth knowing which of your inputs the answer actually hinges on, and which barely move it.

Current-carrying conductors in the raceway	Adjusted table ampacity
2	35.0
2	35.0
3 example above	35.0
5	28.0
6	28.0

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

Wire size: Choose from 14 AWG, 12 AWG, 10 AWG, 8 AWG, 6 AWG, 4 AWG, 3 AWG, 2 AWG, 1 AWG, 1/0 AWG, 2/0 AWG, 3/0 AWG, 4/0 AWG.
Conductor: Choose from Copper, Aluminium.
Ambient temperature: Choose from Up to 30 C / 86 F (factor 1.00), 40 C / 104 F (factor 0.88), 45 C / 113 F (factor 0.82), 50 C / 122 F (factor 0.75), 55 C / 131 F (factor 0.67).
Current-carrying conductors in the raceway: A number, between 1 and 40, starting at 3.

What the results tell you

Result	What it is
Adjusted table ampacity	The headline result. A decimal figure.
Table ampacity at 75 C	A number.
Temperature factor	A decimal figure.
Conductor count factor	A decimal figure.

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.

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