WireGaugeCalc Free calculator · NEC cited · works offline
100a Wire Size @12v
100a wire size @12v is simple with WireGaugeCalc, since it sizes the conductor for 100 amps and checks the drop on a 12 volt run where every volt counts.
You enter the run length and conductor material, and the tool returns the AWG that holds 100 amps while keeping the voltage drop within your target.
That means a 12 volt circuit gets enough copper to run the load without sagging at the far end.
Open the calculatorSmallest conductor whose ampacity meets the load, NEC Table 310.16. Field aid only, verify against the current NEC and your local authority having jurisdiction.
Why 12 volt runs need extra copper
At 12 volts a small drop is a big percentage, so a 0.36 volt loss is already 3 percent of the supply.
Voltage drop rises with run length and current, so 100 amps over a long path can force a much larger conductor than ampacity alone.
The wire size calculator factors the round trip length, so the size it returns holds 12 volts close enough at the load.
Sizing 100 amps on a 12 volt circuit
The calculator balances ampacity and voltage drop together:
- Run length, counted as the round trip distance
- Conductor material, copper or aluminum
- Base ampacity that carries 100 amps
- Voltage drop held near the 3 percent target
- Larger size selected when the run is long
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 wire so large for 100 amps at 12 volts?
At 12 volts even a small voltage drop is a large percentage of the supply, so a longer 100 amp run needs heavier copper to keep the load voltage up. The calculator upsizes the conductor as the run gets longer.
Does NEC ampacity still apply at 12 volts?
Ampacity from NEC 310.16 is set by the conductor and temperature, not the voltage, so 100 amps needs the same base size at 12 volts as at 120 volts. Voltage drop usually drives the size larger on 12 volt runs.
What voltage drop should I aim for at 12 volts?
A 3 percent target keeps the drop under about 0.36 volts so the load runs right. For installed circuits, verify the sizing 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.