Key takeaways
- Daily Wh = the sum of each appliance's watts × hours per day.
- Peak load = every appliance's running watts added up — the worst case your inverter must carry.
- Average load = daily Wh ÷ 24 hours, useful for sizing continuous draw.
- The example loads total 2,040 Wh/day (2.04 kWh) with a 400 W peak.
How to calculate your off-grid load
An off-grid load calculation — an energy audit — is the first step in every solar and battery project. Before sizing a bank or array, you need an honest number for daily energy use. Build it appliance by appliance: list each device, find its wattage, estimate run time, and multiply. Add every row for your daily watt-hours, the figure that drives the rest of your system.
Daily watt-hours tells you the energy to store and replace each day. Peak load is the instantaneous power your inverter must supply if every appliance runs at once. Size storage from the first number and your inverter from the second.
Worked example: a small cabin
Take the five example loads: fridge 150 W × 8 h = 1,200 Wh, lights 40 W × 5 h = 200 Wh, laptop 60 W × 4 h = 240 Wh, fan 50 W × 6 h = 300 Wh, pump 100 W × 1 h = 100 Wh. Add them: 2,040 Wh per day, or 2.04 kWh. The peak load — every running watt at once — is 400 W, and average draw is 2,040 ÷ 24 ≈ 85 W.
Typical appliance running watts
| Appliance | Typical running watts | Note |
|---|---|---|
| Fridge / freezer | ~150 W | Cycles on and off, not constant |
| LED bulb | ~10 W | Per bulb; count your fixtures |
| Laptop | ~60 W | Less when charged |
| Microwave | ~1,000 W | High surge; short run time |
| Well pump | ~1,000 W | Large startup surge |
| TV | ~80 W | Varies with screen size |
| CPAP | ~60 W | More with a heated humidifier |
Feed your audit into the rest of your system
Your daily Wh feeds every sizing tool. Use it to size storage with the battery bank sizing calculator, check your panels with the solar array sizing calculator, and pick an inverter for your peak load with the solar inverter sizing calculator.
Frequently asked questions
How do I calculate my off-grid power needs?
Multiply each appliance's watts by its hours per day, then add them all up — that sum is your daily watt-hours. A 150 W fridge for 8 hours is 1,200 Wh.
What is the difference between running watts and starting watts?
Running watts is the steady draw; starting (surge) watts is the brief spike motors pull at startup, often 2–3× higher. Energy uses running watts; the inverter must handle the surge.
How do I find an appliance's wattage?
Read the label or nameplate, or multiply its volts × amps. For real numbers, plug it into a Kill-A-Watt meter and read actual consumption.
What does daily watt-hours mean for battery and solar sizing?
It's the foundation: batteries are sized from daily Wh × autonomy ÷ DoD, and arrays are sized to replace those Wh with your sun hours.
Should I include phantom or standby loads?
Yes — standby devices draw small amounts around the clock that add real Wh. Include them as a low-wattage row running 24 hours.
How can I reduce my off-grid load?
Switch to LED and high-efficiency appliances, run heavy loads less, cut phantom draw, and use propane for cooking or heating water.
Appliance wattages here are typical reference values — measure your own with a meter for accuracy. For verified efficiency data see ENERGY STAR appliance data. The Wh, peak, and average calculations are exact arithmetic.
Last reviewed June 2026