UK HOME BACKUP POWER SIZING
UK Backup Power Calculator
Calculate how much backup power your home needs during a power cut. Choose the appliances you want to keep running, set the runtime, and estimate the running watts, surge requirement and battery capacity you need.
CALCULATE YOUR REQUIREMENT
How much backup power do you need?
Add the appliances and essentials you want to keep running, then choose how long they need to operate. The calculator will turn those loads into a practical backup-power target.
UK BACKUP POWER CALCULATOR
What needs to keep running?
Select the appliances that matter during a power cut. Typical cycling and short-use allowances are applied automatically. You can replace our wattage figures with the rating from your own appliance.
Add something else
Custom appliances are treated as running for the full backup period unless you enter a shorter number of hours.
YOUR RESULT
Your backup power requirement
Best-fit backup approach
Suitable options
These products meet or exceed the calculated requirement based on the specifications stored by Backup Power Calculator UK.
Some product links may be affiliate links. This does not change the price you pay.
Your selected loads
Want to keep your results? Please print or write them down — Backup Power Calculator does not receive or store your calculator inputs.
How the calculator sizes it: continuous loads are added together, the single largest additional startup surge is added, then output headroom is applied. Battery capacity includes typical appliance cycling plus inverter/conversion losses and a reserve. Appliance labels and real-world consumption vary, so check manufacturer specifications before buying or connecting backup equipment.
HOW IT WORKS
From appliance loads to the right backup-power size
1
Choose what must stay on
Select essentials such as your fridge/freezer, broadband, heating controls, lighting, home-office equipment and other appliances.
2
Set the runtime
Tell the calculator how long each load needs to run so it can estimate the energy requirement rather than looking at wattage alone.
3
See the required size
Use the calculated running watts, surge requirement and watt-hours to compare suitable batteries, portable power stations or generators.
BACKUP POWER GUIDES
Understand the numbers behind the calculator
Backup Power Sizing
Watts, watt-hours, surge loads, capacity and choosing an appropriate system size.
Appliance Runtime
Fridges, freezers, boilers, broadband, home-office equipment and other common loads.
Guides & Comparisons
Portable power stations, generators, batteries and the practical trade-offs between them.
LATEST GUIDES
Latest backup power guides
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How Long Will a 1000Wh Power Station Last?
A 1000Wh power station may run a 100W load for around 8.5 hours under illustrative assumptions, but real runtime depends on usable energy, wattage, losses, surge demand and duty cycle.
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How Much Backup Power Do You Need for a 24-Hour Power Cut?
Plan backup power for a 24-hour UK power cut by calculating watt-hours, allowing for usable battery capacity and surge, and shedding non-essential loads.
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How Long Will a 1500Wh Battery Last During a Power Cut?
A 1500Wh battery might power a router and lights for many hours, but a heater or kettle can use its energy quickly. Learn how to estimate realistic runtime from appliance wattage, usable capacity, inverter losses and surge demand.
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How Much Backup Power Does a Broadband Router Need?
A broadband router is usually a low-wattage load, but it may need to run for hours during a power cut. Learn how to check router watts, calculate battery runtime and size backup power for fibre equipment, phones and laptops.
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What Size Generator Do I Need for Home Backup?
Adding appliance wattages is only the first step in generator sizing. Learn how to calculate running load, account for starting surge and allow sensible headroom for UK home backup.
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How to Measure an Appliance’s Power Use Before Choosing Backup Power
Learn how to measure an appliance’s power use with a plug-in watt meter, interpret nameplate ratings, separate running watts from surge demand and improve backup-power runtime estimates.