PowerOutageKit

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Backup power calculators

Six free tools for sizing a generator or power station and planning how long it will last. Each one answers a single question and shows its working.

Which calculator do I need?

Your questionUse
What size generator or inverter do I need?Generator sizing
How long will my power station last?Battery runtime
How much battery do I need for everything I want to run?Outage load builder
How much battery keeps the fridge and freezer cold?Fridge and freezer backup
How much fuel should I store?Generator fuel planner
Can solar panels keep my battery topped up?Solar recharge

A sensible order to work through them

  1. List your loads in the outage load builder to get a daily energy figure in watt-hours.
  2. Check the peak in the generator sizing calculator, so you know the running and starting watts your equipment must supply.
  3. Choose a source. For a battery, use the runtime calculator. For a generator, use the fuel planner.
  4. Add a recharge plan with the solar calculator if the outage could outlast your battery.

About the numbers

All six calculators run in your browser. Nothing you type is uploaded or saved. Each page shows its formula and a worked example, and each starting value can be replaced with a reading from your own equipment. If you are unsure which reading to use, the guide on measuring your appliances explains it.