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EV · Sizing tool

Home Charger Sizing

Pick the right home wallbox size. Enter your battery, car onboard AC limit and daily driving — the tool matches you to 3.7, 7.4, 11 or 22 kW and flags when a bigger charger is wasted money.

Recommended charger

3.7 kW (16 A · 1-phase)

Daily need: 9 kWh — refills in 2.7 h at 3.7 kW effective. Full charge from empty: 18 h.

All charger tiers

ChargerEffective kWDaily refillFull chargeFit

3.7 kW (16 A · 1-phase)

Standard UK 16 A socket / 1-phase 230 V. No dedicated install required.

3.72.7 h18 hFits window

7.4 kW (32 A · 1-phase)

Dedicated 32 A circuit, 1-phase 230 V. Most common UK home charger.

7.41.4 h9 hFits window

11 kW (16 A · 3-phase)

3-phase 400 V supply (standard on the EU continent). Half UK homes lack this.

110.9 h6.1 hFits window

22 kW (32 A · 3-phase)

3-phase 400 V, 32 A. Overkill for most EVs — check the car's onboard AC limit.

11

car-limited

0.9 h6.1 hWasted capacity

Formula

Effective kW = min(charger kW, car onboard kW)

Daily kWh needed = daily km × kWh/100 km ÷ 100

Charge time = kWh ÷ effective kW ÷ 0.9 efficiency

AC charging is ~90% efficient (line losses + onboard rectifier heat). DC rapid charging above 50 kW hits 93–95% but isn't relevant to home installations.

FAQ

How do I pick the right home charger size?
Match it to (a) your average daily driving and (b) your grid supply. 30 km/day at 18 kWh/100 km = 5.4 kWh — a 3.7 kW charger tops that up in 90 minutes. 100 km/day = 18 kWh — needs 7.4 kW for a 2.5 h refill or 3.7 kW overnight. Over-sizing wastes money if the car's onboard AC charger caps below the wall unit.
What is the car-side charging limit?
Most EVs have an 11 kW onboard AC charger (Tesla Model 3/Y, VW ID.3/4, Kia EV6). A few cheaper models cap at 7.4 kW (Nissan Leaf, older Renault Zoe). A 22 kW home unit is wasted on an 11 kW car — you get 11 kW peak, not 22.
Do I need 3-phase supply?
For 11+ kW charging, yes. Most of continental Europe is 3-phase by default. The UK is predominantly single-phase — check your consumer unit or ask an electrician before ordering a 3-phase charger. Upgrading to 3-phase can cost £2,000–£5,000.
How long does a full charge take?
Charge time (h) = battery kWh ÷ charger kW × (1 / charger efficiency ~0.9). A 60 kWh battery: 3.7 kW ≈ 18 h, 7.4 kW ≈ 9 h, 11 kW ≈ 6 h, 22 kW ≈ 3 h (if the car accepts it).
Is a smart charger worth it?
Yes for two reasons: (1) it schedules charging into off-peak tariff hours (typically 00:30–04:30) saving 40–70% on electricity cost, and (2) solar-diverting models charge only from surplus PV. Payback under 2 years for a driver on a time-of-use tariff.

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