How to size your campervan electrical system

Start with the appliances you actually want to use. A fridge runs throughout the trip, while lights, a laptop or a water pump may run for only a few hours or minutes each day. This free campervan electrical calculator turns those choices into a daily energy estimate, then helps you compare a leisure battery system with a portable power station.

Select UK or US inside the planner to use the appropriate regional options. Add equipment you already own as well as equipment you plan to buy: both draw energy from the same supply. You can adjust each appliance’s running power, quantity and daily use. Where you have a measured daily consumption figure, use that instead of a generic estimate.

How the calculator works

Describe your trip. Choose your region, days away, season and charging options. Solar, driving and shore power affect how much stored energy you need between charges.
Add your appliances. Check the assumptions for each item. Daily energy is power in watts multiplied by hours of use; multiple items are added together.
Get your kit. See the battery energy, power demand and recharge your plan needs, and the system that covers it, priced part by part. An inverter must support the appliances running together and any startup surge, as well as the daily energy demand.
Get your wiring diagram. Enter your email and the design studio opens: your planning diagram, a parts schedule, a forecast and detailed build guides. Enter your email to save and receive your plan. Product offers and build notes are a separate optional signup.

A worked daily energy example

Suppose your fridge uses a measured 400 Wh per day, a laptop draws 60 W for two hours, and your lights draw 10 W for five hours. The daily appliance total is 400 + (60 × 2) + (10 × 5) = 570 Wh. Two days without charging need 1,140 Wh delivered to those appliances.

At a nominal 12.8 V, 1,140 Wh is about 89 Ah of energy. That is an idealised energy conversion, not a battery recommendation. The selected system also needs allowance for usable battery capacity, conversion losses, reserve and the conditions on your trip. Add your own appliances to the calculator to see how those assumptions change your result.

Frequently asked questions

What is the difference between watts, watt-hours and amp-hours?

Watts describe power at a moment in time. Watt-hours describe energy used over time. Amp-hours describe battery charge at a stated voltage: multiply amp-hours by nominal volts to compare battery energy in watt-hours.

Can solar cover all my daily use?

Sometimes, but output depends on location, season, shade and weather. Compare the forecast with your daily demand and plan for periods of low generation. Read the campervan solar setup guide for the decisions behind a solar system.

Does a bigger battery let me run any appliance?

No. Stored energy determines runtime; inverter output and battery discharge limits determine which loads can run. Startup surges can exceed normal running power. Check the actual equipment ratings and the warnings in your plan.

Is this a final installation design?

The result is a planning estimate. Cable routes, installation conditions, protective devices and equipment compatibility still need checking for your vehicle. Use the complete electrical system guide and wiring safety guide to prepare for that review.