VANPOWERCALC

12V Wire Gauge Calculator

Determine the correct AWG or mm2 wire size for your campervan 12V electrical system to prevent voltage drop.

Input your amps and wire length to find the exact wire cross-section required. Critical for DIY van builds.
Keep your voltage drop under 3% for optimal performance of 12V fridges and Maxxair fans. Safety first!
⚡ Expert tip
Always measure your actual cable runs with a tape measure — don't estimate. Route planning around panels and cabinet edges typically adds 15-25% more length than a straight-line estimate. Running short on cable mid-build means mid-run joins that add resistance and potential failure points.

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Comparison table

CurrentLength 1mLength 2mLength 5mLength 10m
10A18 AWG18 AWG16 AWG14 AWG
20A16 AWG14 AWG12 AWG10 AWG
30A14 AWG12 AWG10 AWG8 AWG
50A10 AWG8 AWG6 AWG4 AWG
100A6 AWG4 AWG2 AWG1/0 AWG

About this tool

Van 12V Wire Size Calculator: Complete Guide with Tables

Correct wire sizing for your van electrical system is not optional — an undersized cable running too much current gets hot, melts insulation, and can start a fire. Here's a practical reference with exact sizing for every common van application.

Wire Size by Application (12V System)

Application Typical Current Max Run Length (3% drop) Wire Size
LED lighting circuit 5-10A Up to 10m 1.5mm² (16 AWG)
USB charging circuit 5-10A Up to 6m 2.5mm² (14 AWG)
12V water pump 7-10A Up to 5m 2.5-4mm²
12V fridge 10-15A Up to 4m 4mm² (12 AWG)
MPPT output (30A) 30A Up to 3m 6mm² (10 AWG)
DC-DC charger (40A) 40A Up to 2m 10mm² (8 AWG)
Inverter 1,000W ~90A peak Under 0.5m 25mm² (4 AWG)
Inverter 2,000W ~180A peak Under 0.4m 50mm² (1/0 AWG)
Inverter 3,000W ~270A peak Under 0.3m 70mm² (2/0 AWG)
Battery main cables varies Under 0.5m 35-70mm²

The 3% Voltage Drop Rule

For any 12V system, keep voltage drop below 3% (0.36V). More than this and:

  • Fridges cycle off unexpectedly
  • Inverters trigger low-voltage protection
  • Devices charge slowly

Voltage drop formula: V_drop = Current (A) × Length (m, both directions) × Resistance (Ω/m) Resistance for copper cable: 6mm² ≈ 0.0033 Ω/m, 4mm² ≈ 0.0050 Ω/m, 2.5mm² ≈ 0.0079 Ω/m

Example: 10A run at 4m one-way (8m total), 1.5mm² cable: 10 × 8 × 0.013 = 1.04V = 8.7% drop — WAY too much. Use 4mm² instead: 10 × 8 × 0.005 = 0.4V = 3.3% — acceptable.

Fuse Sizing for Each Circuit

Every positive cable needs a fuse as close to the battery positive terminal as possible:

Wire Size Fuse Rating
1.5mm² 10-15A
2.5mm² 16-25A
4mm² 30-40A
6mm² 40-50A
10mm² 60-80A
25mm² 125-150A
50mm² 200-250A

Cable Quality: Tinned Copper vs Standard

For van environments with moisture, condensation and temperature cycling, use tinned copper marine-grade cable. Standard automotive copper cable oxidizes over time, increasing resistance and heat. The premium (typically +20-30% cost) is worth it for a long-lived, reliable system.

Expert tip: Always measure your actual cable run length — don't estimate. Include routing around corners, behind panels, and add 20% for the connector/terminal portion at each end. Many builds end up 15-25% short on cable length, forcing joins mid-run that add resistance.

Frequently asked questions

What wire size do I use for a 30A MPPT to battery run in a van?▼
For a 30A MPPT, use 6mm² (10 AWG) cable for runs up to 3m. For longer runs (3-6m), step up to 10mm² (8 AWG). Keep voltage drop below 3% (0.36V at 12V).
What size cable do I need for a 12V compressor fridge?▼
A 12V fridge typically draws 10-15A maximum. Use 4mm² (12 AWG) for runs up to 4m, 6mm² for longer runs. Add a 15-20A inline fuse or blade fuse holder as close to the battery as possible.
Can I join cables mid-run in a van electrical system?▼
Avoid it. Every joint adds resistance and potential failure points. If joins are unavoidable, use proper waterproof butt connectors with adhesive heat shrink — not crimp connectors without adhesive in a potentially damp van environment.
What is the difference between single-stranded and multi-stranded van cable?▼
Always use multi-stranded (flexible) cable for van installations. Single-stranded wire fatigues and breaks when subjected to vehicle vibration. Marine-grade tinned multi-strand copper cable is the industry standard for van builds.

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