All calculators (10)
Pick the question you're trying to answer. Each calculator explains its formula, lists common values and flags the mistakes people usually make.
By Zubair Abid. Updated .
How the tools are organised
The tools are grouped by job: batteries and runtime (how long will it last), charging (how long to refill, which charger, airline limits), home energy (running cost and solar sizing) and screens (pixel density and size). If you're not sure where to start, begin with the runtime calculator.
Batteries & runtime
Charging
Home energy
Screens
Which calculator do I need?
| Your question | Use this |
|---|---|
| How long will my power station run my devices? | Power station runtime |
| How many hours of backup from my inverter battery? | UPS backup time |
| How many solar panels and batteries do I need? | Solar panel size |
| What does this appliance cost to run? | Electricity cost |
| Can I take this power bank on a plane? | Power bank airline checker |
| How many phone charges from my power bank? | Power bank charges |
| How many Wh is this mAh battery? | mAh to Wh converter |
| How long will it take to charge? | Charging time |
| Is this USB-C charger enough for my laptop? | Laptop charger checker |
| How sharp is this monitor or TV? | Screen PPI |
The units behind every tool
Watts (W) measure power: how fast energy is used or delivered right now. A 60 W laptop charger can deliver up to 60 watts at any moment.
Watt-hours (Wh) measure energy: power multiplied by time. A 1,000 Wh battery can, in theory, supply 100 W for 10 hours. Kilowatt-hours (kWh) are the same unit × 1,000 and are what electricity bills count.
mAh and Ah measure electric charge. They only become energy when multiplied by voltage: Wh = Ah × V. That's why two batteries with the same mAh can hold very different amounts of energy, and why the mAh to Wh converter asks for voltage.
Efficiency is the share of energy that survives conversion. Turning battery DC into AC, stepping USB voltages up and down, and charging a battery all waste some energy as heat. Our tools apply realistic efficiency values rather than assuming a perfect 100%.
What the calculators can't know
A calculator can't see your specific fridge, your battery's age or the temperature in your garage. Each of these can move the real result by 10 to 30%. Where it matters most (motor start-up surges, medical equipment, airline rules), the tools show a warning next to the result.
For safety-critical decisions, such as powering medical devices or wiring a home solar system, use these results for planning and confirm with the manufacturer or a qualified electrician.