EV charger wire calculator
Charger power, voltage, system, length and maximum drop: you get current, 125% design current, copper wire size and the recommended breaker.
Minimum wire size
10 mm²
- Minimum copper cross-section10 mm²
- Charger current32.17 A
- Design current (× 1.25)40.22 A
- Recommended breaker50 A
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How it's calculated (visible formula)
I = P ÷ V (or ÷ √3·V); design I = 1.25 × I; size = max(by voltage drop; by ampacity)
- Net geometric measurement, no waste.
- Adjustable waste % for cuts and breakage.
- Purchase rounded up to sellable units (boxes, bags, buckets, boards).
How to calculate it, step by step
- Enter charger power (e.g., 7.7, 9.6, 11.5 kW).
- Choose single-phase or three-phase and the voltage.
- Work out current and multiply by 1.25 (continuous load).
- Measure run length from the panel to the charger.
- Size wire by drop and ampacity, then pick the breaker.
Worked example: 7.7 kW (32 A) charger on 240 V, 66 ft
- I = 7,700 ÷ 240 = 32 A
- Design: 40 A
- By ampacity: 10 mm² (≈ 8 AWG)
→ 8 AWG copper on a 40 A breaker (6 AWG for long runs).
Common mistakes
- Sizing a multi-hour load at 100%.
- Skipping GFCI protection where required.
- Sharing the circuit with other loads.
Pro tips
- Run a dedicated circuit for the charger.
- Follow the charger's GFCI requirements.
- Check service capacity; a load manager can avoid a panel upgrade.
- Pull oversized conduit for a future upgrade.
From calculation to quote
Add labour, overhead and your margin, and generate the professional PDF.
FAQs
- What wire for a 40 A EV charger?
- 8 AWG copper is typical; 6 AWG for long runs or in conduit.
- Why 125%?
- EV charging is a continuous load (NEC 625.41).
- What breaker for a 48 A charger?
- 60 A with 6 AWG copper.
- Can I install an EV charger myself?
- Many areas require a licensed electrician and permit for a 240 V circuit.
- How long does a 7.7 kW charger take?
- About 25–30 miles of range per hour.
- Can I use a 120 V outlet?
- Level 1 works for low daily mileage; Level 2 is better for daily use.
Sources and standards
Maintained by Srikanta M · Formula v1.0.0 · Verified 2026-09-10 · Updated 2026-09-10 · Limits: quantity estimation, not structural design or site supervision.