WireGaugeCalc Free calculator · NEC cited · works offline
Calculate Ampacity Of 12 AWG
Calculate ampacity of 12 awg is quick with WireGaugeCalc, since you choose the conductor material and termination temperature and read the rated amps.
It pulls the value straight from the NEC 310.16 column that matches your terminals.
You get the usable ampacity at a glance, so you can confirm the breaker and wire agree.
Open the calculatorAllowable ampacity from NEC Table 310.16 at the chosen termination temperature. Field aid only, verify against the current NEC and your local authority having jurisdiction.
The Calculated Ampacity Of 12 AWG By Temperature Column
12 AWG copper shows 20 amps in the 60 degree C column, 25 amps in the 75 degree C column, and 30 amps in the 90 degree C column.
Most equipment terminals are rated 75 degrees C, so the usable value is the one tied to those terminations.
The small-conductor rule in 240.4(D) still limits 12 AWG copper to a 20 amp overcurrent device in most cases.
How WireGaugeCalc Finds The Ampacity
Pick the details and the tool returns the rated current:
- Conductor size set to 12 AWG
- Copper or aluminum material
- 60, 75, or 90 degree C termination column
- NEC 310.16 table value
- 240.4(D) small-conductor limit reminder
One app for every NEC calculation
WireGaugeCalc keeps the calculations you reach for most in one place:
- Voltage drop and wire sizing for any run
- Conduit fill for EMT, PVC, and RMC
- Box fill and junction box sizing
- Ampacity and temperature derating
- Motor circuit and load calculations
- Conduit bend offsets and saddles
Built for the field, works offline
The whole app runs on your phone, so it keeps working in a basement, an attic, or a job site with no signal.
There is no account to create and nothing to load. Open it, run the number, and get back to work.
- No signup and no signal needed
- Answers in a tap, not a spreadsheet
- Same tool on phone, tablet, and desktop
Every result cites the NEC article
Each answer shows the table or formula it came from, so you can check the method and learn the code as you go.
That makes the app useful on the job and during exam prep, since the reasoning is right next to the number.
Switch the code year your job runs on
Jurisdictions adopt the NEC at different times, so you can match the calculation to the code in force:
- NEC 2017, 2020, and 2023 tables
- Copper and aluminum conductors
- 60, 75, and 90 degree C terminations
- Single-phase and three-phase systems
Run the number, then get back to work
Stop flipping through a paper book or hopping between calculator sites. Enter your values, read the code-cited answer, and move on. Free to use, no signup.
Open the calculatorFrequently asked questions
Why is 12 AWG copper limited to 20 amps if the 90 degree column shows 30?
The 90 degree C ampacity is used for derating math, but NEC 240.4(D) caps 12 AWG copper at a 20 amp overcurrent device. The higher column rarely sets the breaker.
Which temperature column should I use to calculate the ampacity of 12 AWG?
Use the column that matches the lowest rated terminal in the circuit, usually 75 degrees C. Always verify the correct column against the current NEC and your local authority having jurisdiction.
Is WireGaugeCalc free to use?
Yes. Every calculator is free to run with no signup. A paid tier adds saved projects, PDF reports, and extra code years, but the core math stays free.
Does it work without internet?
Yes. The app runs on your device, so it keeps working with no signal on a job site, in a basement, or in an attic.
Are the results code accurate?
Results follow published NEC tables and standard formulas, and each answer shows the article it came from. It is a field aid, not a stamp of approval, so verify against the current code and your local authority before you wire anything.
Which NEC code year does it use?
You can switch between NEC 2017, 2020, and 2023, since jurisdictions adopt the code at different times. Pick the year your job runs on.