Will it run, and for how long?

Why these calculators exist

Most battery and power questions come down to three numbers: how much energy is stored (watt-hours), how fast something uses it (watts) and how much is lost along the way. The trouble is that products are labelled inconsistently. Power banks list mAh, power stations list Wh, inverter batteries list Ah, and chargers list watts. Airlines write their rules in Wh. Your electricity bill counts kWh, or 'units'.

Each tool here converts those labels into the answer you actually need: hours of runtime, the number of panels to buy, the cost per month, whether a charger is strong enough, or whether you can board a plane with your power bank.

How to get an accurate answer

1. Read the label. Capacity, voltage and watts are almost always printed on the device, the battery or the charger.
2. Use average power, not the maximum. Fridges, fans and pumps cycle on and off. A plug-in energy meter gives the real figure.
3. Keep the defaults unless you know better. Efficiency and reserve values are set to realistic middle values, not best-case marketing numbers.
4. Read the notes under the result. They flag overloads, start-up surges, airline limits and other things that change the answer.

If you want to understand the reasoning behind the defaults, the how we calculate page explains every assumption and where it comes from.

Who uses these tools

People preparing for power cuts use the power station runtime and UPS backup calculators to plan what they can keep running. In Pakistan and India, where scheduled load-shedding is common, the UPS tool is built around the 12 V, 24 V and 48 V lead-acid and lithium batteries sold locally.

Travellers check their power bank against airline limits before packing. Homeowners size a solar system or work out which appliance is quietly adding to the bill. Anyone choosing a new monitor or laptop charger can compare options on equal terms before buying.

What we promise

• No data collection from the tools. Calculations happen in your browser; the numbers you type aren't sent anywhere.
• Formulas on every page, with a worked example you can check by hand.
• Conservative defaults. We'd rather you plan for a little less runtime than be caught out.
• Corrections welcome. If you spot a mistake, tell us and we'll fix it and update the date.