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Watt Hour Calculator

Watt Hour Calculator

Find out how many watt-hours your devices use per day and how big a battery power station you need to get through an outage.

Sized for real outages
Inverter losses included
mAh and Ah converter

01 List your devices watts × hours per day

Device	Watts	Hrs/day	Qty	Wh/day	Remove

Quick add:

02 How long should it last?

Days without recharging 1 = a full day of outage. Use 0.5 for an evening.

Convert mAh or Ah to watt-hours

mAh

Volts

Watt-hours

Wh = mAh × V ÷ 1,000. A "20,000 mAh" power bank at 3.7 V holds 74 Wh. For amp-hours (Ah), Wh = Ah × V: a 100 Ah, 12 V battery holds 1,200 Wh.

How to calculate watt-hours

Watt-hours (Wh) = watts × hours of use

Find each device's watts on its label or charger. For fridges, freezers and pumps use the average watts (they cycle on and off): the quick-add list does this for you.
Multiply by the hours you'll use it per day and add everything up.
Divide by 0.85 to cover inverter losses, then multiply by the days you want to last. That's the capacity your power station needs.

Example: a fridge (60 W average × 24 h = 1,440 Wh), Wi-Fi (20 W × 24 h = 480 Wh) and LED lights (100 W × 5 h = 500 Wh) use 2,420 Wh per day. For one day without power you need about 2,420 ÷ 0.85 = 2,850 Wh of battery, so a 3,000 Wh class power station, or a 2,000 Wh unit plus a few hours of solar charging.

How long does each power station last?

Calculated from each model's rated capacity with 85% usable after inverter losses. Real runtime varies with temperature, battery age and how hard your devices work.

Power station	Capacity	Fridge only	Fridge + Wi-Fi + lights	CPAP (with humidifier, 8 h/night)	Laptop + monitor
EcoFlow RIVER 3 Plus	286 Wh	4.1 hours	2.3 hours	0.3 nights	2.0 hours
Jackery Explorer 300 Plus	288 Wh	4.1 hours	2.3 hours	0.3 nights	2.0 hours
EcoFlow DELTA 3 Plus	1,024 Wh	15 hours	8.3 hours	1.2 nights	7.3 hours
Anker SOLIX C1000 Gen 2	1,024 Wh	15 hours	8.3 hours	1.2 nights	7.3 hours
Jackery Explorer 1000 v2	1,070 Wh	15 hours	8.7 hours	1.3 nights	7.6 hours
BLUETTI AC180	1,152 Wh	16 hours	9.3 hours	1.4 nights	8.2 hours
Jackery Explorer 2000 v2	2,042 Wh	29 hours	17 hours	2.4 nights	14 hours
EcoFlow DELTA 2 Max	2,048 Wh	29 hours	17 hours	2.4 nights	15 hours
Anker SOLIX C2000 Gen 2	2,048 Wh	29 hours	17 hours	2.4 nights	15 hours
BLUETTI AC200L	2,048 Wh	29 hours	17 hours	2.4 nights	15 hours
DJI Power 2000	2,048 Wh	29 hours	17 hours	2.4 nights	15 hours
BLUETTI Elite 200 V2	2,074 Wh	29 hours	17 hours	2.4 nights	15 hours
Jackery HomePower 3000	3,072 Wh	44 hours	25 hours	3.6 nights	22 hours
Anker SOLIX F3800 Plus	3,840 Wh	2.3 days	31 hours	4.5 nights	27 hours
EcoFlow DELTA Pro 3	4,096 Wh	2.4 days	33 hours	4.8 nights	29 hours

Frequently asked questions

How do I calculate watt-hours?

Multiply the power in watts by the hours of use: a 100-watt device running for 5 hours uses 500 watt-hours (Wh). Add up all your devices to get your daily total. 1,000 Wh is 1 kilowatt-hour (kWh), the unit on your electric bill.

How long will a 1,000 Wh power station last?

Divide the usable energy by the load. A 1,000 Wh unit delivers about 850 Wh after inverter losses, so it runs a 100-watt load for about 8.5 hours, or a modern refrigerator (about 60 watts on average, since the compressor cycles) for around 14 hours.

How do I convert mAh to watt-hours?

Multiply mAh by the voltage and divide by 1,000. A 10,000 mAh phone power bank at 3.7 volts holds 37 Wh. Airlines usually allow power banks up to 100 Wh in carry-on bags without approval.

Why do fridges use fewer watts than their label says?

A refrigerator compressor turns on and off. It may draw 150 watts while running, but only runs about 40% of the time, so its average is about 60 watts. For energy (watt-hours) use the average; for sizing the output and surge use the running and starting watts, which our generator size planner handles.

Capacities are manufacturer ratings, last checked October 21, 2026. See how we pick. As an Amazon Associate I earn from qualifying purchases.