Wire, cable & gauge
12V wire size calculator: AWG & mm²
Enter the continuous current and one-way cable length. Compare the size needed for ampacity with the size needed for voltage drop, then open that circuit in Crimp.
12 V / 24 V DC planning · reviewed 11 September 2026 · ABYC E-11 table basis
Use the circuit's design voltage, usually 12 or 24 V. Supported range: 1–60 V DC.
Maximum continuous operating current. This tool adds 25% ampacity headroom; it does not size motor-start or cranking circuits.
Measure from source to load along the cable route. We add an equal-length return: 5 m here means 10 m of circuit conductor.
Copper only. A 105°C jacket rating is not a permissible terminal temperature.
Use the worst section of the route. Engine-space calculation uses the existing conservative 0.82 ampacity multiplier.
Count current-carrying positive and return conductors. A bundle needs a documented factor; it is not inferred from count alone.
Wire size is unknown
Still needed
- Circuit voltage (V)
- Continuous current (A)
- One-way length (m)
- Voltage-drop allowance
- Insulation rating
- Temperature / engine space
- Conductor routing
Fuse selection is separate. No fuse is selected, placed or verified by this wire result. Check the fuse and holder.
Worked calculation
A longer run can need more copper.
Synthetic example: 20 A continuous at 12 V, 5 m one way plus an equal return, 3% allowance, 105°C copper outside engine spaces at up to 30°C, up to two conductors.
Metric conductor
10 mm²
Voltage drop determines this size
- Ampacity constraint, including 125% headroom
- 25.00 A → 1.5 mm²
- Voltage-drop constraint
- 9.72 mm² minimum → 10 mm²
- Selected conductor area
- 10.00 mm²
- Installed ampacity after derating
- 80.00 A (factor 1.000)
- Voltage drop, outgoing plus equal return
- 0.350 V / 2.92%
AWG conductor
AWG 6
Voltage drop determines this size
- Ampacity constraint, including 125% headroom
- 25.00 A → AWG 14
- Voltage-drop constraint
- 9.72 mm² minimum → AWG 6
- Selected conductor area
- 13.30 mm²
- Installed ampacity after derating
- 80.00 A (factor 1.000)
- Voltage drop, outgoing plus equal return
- 0.263 V / 2.19%
Method and limits
Check both constraints before choosing wire.
For this continuous DC branch, required ampacity is current × 1.25. Available ampacity is the table value × temperature factor × documented bundle factor. Voltage drop is 2 × current × one-way length × copper resistivity ÷ area; the model uses 0.0175 Ω·mm²/m at 25°C. It does not model hotter copper resistance, terminal loss or unequal/shared returns.
We compare the smallest table conductor meeting each constraint, then choose the larger. Both can require the same table step. The 1.5 mm² mechanical floor can decide small circuits. If no available size meets both constraints, the result stays outside the table; the largest wire is not presented as sufficient.
Metric mode uses Crimp’s existing table. AWG mode uses actual nominal AWG areas with conservative ampacity taken from the next smaller metric entry. This keeps the same 1.5 mm² floor, so AWG selections start at 14 AWG. It can oversize compared with a native AWG ampacity table. Changing units preserves physical length but can change the selected conductor. Existing diagram pages still use approximate AWG counterparts; 16 mm² and 6 AWG are different areas.
Lower insulation ratings, hotter routes, conduit and thermal insulation are outside this calculator. Do not choose a cooler condition to get a result. Manufacturer terminal ratings, minimum wire, surge behavior, protection, cable construction and your governing installation rules still need review. The pinned wire and total factor follow you into the editor; review both after edits.
ABYC E-11 is the implemented table basis. Marine wire gauge, RV wire size, campervan cable size and Australian dual-battery wording do not establish UK or AS/NZS standards coverage.
Sources