The kWh Calculator converts between watts, hours, kilowatt-hours, and electricity cost in four bidirectional modes. 'Watts + Time' converts wattage and usage duration into kWh and cost, with 5 time units (minutes, hours, days, weeks, months) and full day/month/year breakdowns. 'kWh + Time' works backwards to find devic..
Enter wattage and usage time — get energy in kWh and electricity cost.
= 6.00 hours
RESULT
ENERGY USED
9.000
kWh = 9,000.00 Wh
COST
$1.350
ENERGY VISUALISER
FULL SUMMARY
FORMULA
QUICK REFERENCE — kWh PER DAY (8 hrs)
Choose your calculation mode. 'Watts + Time → kWh' is the most common — enter a device's wattage and how long you run it to get energy in kWh and cost. 'kWh + Time → Watts' works backwards: if you know how many kWh were consumed and the duration, it tells you the wattage of the device. 'kWh + Watts → Hours' tells you how long a device ran, or how long you can run it on a given energy allowance. 'Cost → kWh' converts a dollar amount into kWh at your electricity rate.
In Watts + Time mode, enter the device wattage (found on the label or spec sheet) and the time period. The time unit selector supports minutes, hours, days, weeks, and months — useful for calculating annual cost directly. The calculator shows how many hours the time period converts to for transparency.
Enter your electricity rate in $/kWh. Use the preset buttons for common rates, or enter your exact rate from your electricity bill. The rate is used to calculate cost in all four modes.
Read the results: in Watts + Time mode you get kWh, watt-hours (Wh), cost for the session, and if hours are chosen, a full breakdown of daily, monthly, and yearly kWh and cost. The dark energy visualiser on the right shows lightning bolts scaled to the energy amount, colour-coded green (low) to red (high power).
The formulas panel shows all four conversion formulas at a glance. The quick reference table shows typical daily kWh for common appliances at standard usage hours — useful for cross-checking your inputs.
Four kWh calculator examples: EXAMPLE 1 — Watts + Hours → kWh A 1,500W space heater runs 6 hours/day for 30 days: • kWh = 1,500 × 6 ÷ 1,000 = 9 kWh/day • Monthly: 9 × 30 = 270 kWh • Cost at $0.15/kWh: 270 × $0.15 = $40.50/month EXAMPLE 2 — kWh + Hours → Watts Your meter shows 12 kWh used over 8 hours. What was running? • Watts = 12 × 1,000 ÷ 8 = 1,500W Answer: likely a 1,500W space heater or similar appliance. EXAMPLE 3 — kWh + Watts → Hours You have 5 kWh of solar battery charge. A 500W device needs power. • Hours = 5 × 1,000 ÷ 500 = 10 hours Answer: you can run a 500W device for 10 hours on 5 kWh. EXAMPLE 4 — Cost → kWh Your electricity bill shows a charge of $45 for the period. Your rate is $0.15/kWh. • kWh = $45 ÷ $0.15 = 300 kWh consumed
Last updated: April 29, 2026 · Formula verified by EagleCalculator team · Eagle-eyed accuracy for every calculation.