About WattWise

WattWise is a free, browser-based backup power runtime estimator. Whether you're preparing for load shedding, planning an off-grid setup, or just want to know how long your gear will last when the grid goes down — WattWise gives you a clear, real-time answer.

What It Does

Enter your power source and the appliances you want to run. WattWise calculates how long your power will last, how much it costs per session, and how that compares to grid electricity.

No sign-up. No server. Everything runs in your browser and your settings are saved locally.

Two Calculation Modes

Fuel Generator

Select a generator preset (1–7.5 kVA) or enter your own rated capacity and burn rate. Provide the tank volume in litres or gallons and WattWise tells you exactly how many hours of runtime you have left.

The optional appliance panel lets you track your total load against the generator's rated output, so you can see at a glance whether you're running efficiently or risking an overload.

Battery Power Station

Choose from popular presets — including models from EcoFlow, Jackery, and Bluetti — or enter a custom capacity in watt-hours. WattWise factors in inverter efficiency to give you a realistic discharge estimate.

If you have solar panels, the solar input panel lets you configure your array and see how much it offsets your battery draw. When solar fully covers your load, WattWise shows an infinite runtime — because you're no longer depleting the battery at all.

Appliance Library

WattWise ships with 51 common household and office appliances across 10 categories:

• Refrigeration — bar fridges, full-size fridges, chest freezers
• Climate Control — fans, air conditioners, heaters, electric blankets
• Lighting — LED bulbs, tubes, strips, downlights, flood lights
• Entertainment — TVs, projectors, gaming consoles, sound systems
• Computing & Networking — laptops, desktops, monitors, routers, NAS devices
• Kitchen — microwaves, kettles, toasters, air fryers, coffee makers
• Health & Medical — CPAP machines, oxygen concentrators, nebulizers
• Security & Safety — cameras, alarm systems, electric fences, baby monitors
• Charging — phone, tablet, and laptop chargers
• Pumps & Motors — borehole pumps, pool pumps, washing machines

Can't find what you need? Add any appliance by name and wattage using the custom appliance form.

Cost Comparison

The optional cost comparison card breaks down what a session costs in fuel or battery charging versus what the equivalent grid electricity would cost. It supports 12 currencies out of the box, with a custom entry if yours isn't listed.

Your Data Stays with You

All settings, appliance selections, and custom appliances are saved to your browser's local storage. Nothing is sent to a server. Clearing your browser data or pressing the reset button will wipe your saved state.

Accuracy and Limitations

WattWise produces estimates based on the values you provide. Real-world runtime will vary depending on:

• Actual appliance draw versus nameplate wattage
• Ambient temperature and fuel quality (for generators)
• Battery health and age (for power stations)
• Variable solar irradiance

Use WattWise as a planning tool, not as a substitute for reading your equipment's manual.