Free watt hour calculator to convert watts to watt-hours, estimate battery runtime, calculate electricity costs, and size solar panel systems. Plan your energy needs accurately.
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Understanding watt hours is essential for sizing batteries, estimating electricity costs, and planning solar systems. Our calculator handles everything from basic Wh calculations to full solar panel sizing with battery recommendations.
A watt hour (Wh) measures energy consumption over time. It's calculated by multiplying power (watts) by time (hours). A 100W device running for 5 hours uses 500Wh or 0.5kWh. This unit helps compare batteries, calculate electricity bills, and size renewable energy systems.
Watt Hour Formula
Wh = Watts ร HoursChoose the right portable power station or UPS by matching battery Wh capacity to your device requirements.
Identify energy-hungry appliances and calculate their monthly/yearly operating costs.
Properly size solar panels and batteries based on daily energy needs and available sunlight.
50W laptop on 500Wh battery = 8.5 hours runtime (at 85% efficiency).
50W mini fridge ร 24h ร 30 days = 36kWh/month โ $4.30 at $0.12/kWh.
5000Wh daily use รท 5 sun hours = 1250W solar panels needed (plus 20% buffer).
400Wh daily use ร 2 days autonomy = 800Wh minimum battery capacity.
Watts (W) measure power - how fast energy is used. Watt hours (Wh) measure total energy consumed. A 100W bulb uses 100 watts of power; running it for 10 hours uses 1000Wh (1kWh) of energy.
Check the label on the device or its power adapter. It shows watts (W) or amps (A) and volts (V). Multiply A ร V to get watts. For variable loads like laptops, use typical wattage (30-50W), not max rated power.
Batteries and inverters lose 10-20% of energy as heat during conversion. A 500Wh battery with 85% efficiency provides only ~425Wh of usable power. Always account for this when sizing systems.
Peak sun hours (PSH) vary by location and season. Arizona averages 6-7 PSH, while Seattle gets 3-4 PSH. Check solar insolation maps for your area. Use conservative estimates for reliable system sizing.