kWh Calculator

kWh Calculator

Calculate kilowatt-hours from watts, hours, and days — the same math your utility meter runs on — with an optional cost estimate and a real-world derating factor for equipment that rarely performs at its nameplate rating. This calculator also converts the other direction, from a known kWh total back to average watts, and handles battery Amp-hour (Ah) conversions both ways for sizing an inverter, solar bank, or backup system. Pick a common appliance from the dropdown for an instant wattage fill, or browse the full searchable reference table below. A comparison chart and printable output are included for job-site documentation.

Use Watts → kWh for everyday energy-use and cost estimates, kWh → Watts to back-calculate an average power draw, and the Ah modes to convert a known energy amount to or from battery Amp-hours at a given system voltage.

Comparing several appliances at once, or need a full monthly bill estimate? Use the Electrical Cost Calculator →

Formula: kWh = (Watts × Hours) ÷ 1,000, applied per day, month, and year. Add a rate for a cost estimate, or a derating factor to adjust for real-world conditions.

Common Appliance — auto-fills typical wattage

Power — select unit if not watts

Hours per Day

Custom Period (Days) — optional, for a total over N days

Electricity Rate ($/kWh) — optional, for cost estimate

Derating / Efficiency Factor — optional, 1.0 = ideal conditions

Energy per Day

—

kWh

Energy per Month

—

kWh (× 30 days)

Energy per Year

—

kWh (× 365 days)

Est. Monthly Cost

—

USD

Formula: —

Comparison

Results are for reference and estimation only. Verify all values before use in any electrical design, battery sizing, or billing decision. See full disclaimer below.

How to Use the kWh Calculator

Select a Conversion Mode

Choose Watts → kWh for everyday energy-use and cost estimates, kWh → Watts to back-calculate an average power draw, or one of the Ah modes to convert between energy and battery Amp-hours.

Enter Your Values

Type the power, hours, and days — or pick a Common Appliance from the dropdown to auto-fill a typical wattage. Add an optional electricity rate for a cost estimate, and an optional derating factor to adjust for real-world conditions like heat or aging equipment.

Review Results and the Comparison Chart

Click Calculate. Results appear immediately with the exact formula substituted in — on the Watts → kWh tab, a chart also compares your daily, monthly, and yearly totals side by side.

Check the Reference Tables and Print

Expand the kWh Quick Reference Table to sanity-check a result, or the searchable Household Appliance Wattage Reference Table to look up a typical wattage by category — use its Use → button to send a value straight into the calculator. Use Print to capture results as they appear on screen for documentation.

kWh Quick Reference Table

Common watt / hour / day combinations and their resulting energy use, at both single-day and full-month scale. Use this to sanity-check a calculated result at a glance.

Watts	Hours/Day	Days	Result (kWh)
100 W	10 h	1	1 kWh
500 W	2 h	1	1 kWh
1,000 W	1 h	1	1 kWh
1,500 W	4 h	1	6 kWh
2,000 W	5 h	1	10 kWh
3,000 W	3 h	1	9 kWh
1,500 W	4 h	30	180 kWh
4,500 W	2 h	30	270 kWh
5,000 W	6 h	365	10,950 kWh

Tip: divide watts by 1,000 to get kilowatts, then multiply by hours to get kWh for that period. Multiply the daily figure by the number of days for a period total.

Household Appliance Wattage Reference Table 24 Appliances

Typical wattage and daily use for common household appliances. Search or filter by category, then use Use → to send a wattage straight into the Watts → kWh calculator above.

Appliance	Category	Typical Wattage	Typical Daily Use
Refrigerator (Standard)	Kitchen	150 W	24 h (always on)
Chest Freezer	Kitchen	200 W	24 h (always on)
Microwave Oven	Kitchen	1,000 W	~0.1 h
Dishwasher	Kitchen	1,800 W	~1 h
Coffee Maker	Kitchen	900 W	~0.25 h
Window AC Unit	HVAC	1,200 W	~8 h
Central Air Conditioner	HVAC	3,500 W	~8 h
Electric Space Heater	HVAC	1,500 W	~6 h
Ceiling Fan	HVAC	75 W	~8 h
Electric Furnace Blower	HVAC	500 W	~8 h
Washing Machine	Laundry	500 W	~0.75 h
Electric Clothes Dryer	Laundry	3,000 W	~0.75 h
55" LED TV	Entertainment	100 W	~5 h
Gaming Console	Entertainment	150 W	~3 h
Home Theater / Soundbar	Entertainment	60 W	~4 h
Desktop Computer	Office	200 W	~8 h
Laptop Computer	Office	65 W	~8 h
Wi-Fi Router	Office	10 W	24 h (always on)
LED Bulb (60W equivalent)	Lighting	9 W	~5 h
Incandescent Bulb (60W)	Lighting	60 W	~5 h
Electric Water Heater, 40-gal	Water	4,500 W	~2 h
Tankless Electric Water Heater	Water	18,000 W	~1 h
Hair Dryer	Workshop	1,500 W	~0.1 h
Power Drill	Workshop	600 W	~0.25 h

No appliance matched your search. Try a different keyword.

Wattage values are typical nameplate or average running figures and vary by brand, model, and age. Always use the actual nameplate or measured value for critical calculations.

Frequently Asked Questions

How do I calculate kWh from watts?

Multiply the power in watts by the hours used, then divide by 1,000: kWh = (Watts × Hours) ÷ 1,000. For example, a 1,500-watt heater running 4 hours a day uses 6 kWh per day. Multiply the daily figure by 30 for a monthly estimate or 365 for a yearly estimate — this calculator does all three automatically.

How do I convert kWh to Amp-hours (Ah)?

Multiply the energy in kWh by 1,000 to get watt-hours, then divide by the system voltage: Ah = (kWh × 1,000) ÷ Volts. A 2 kWh draw on a 12V battery system equals about 166.7 Ah. Always use the nominal voltage of the actual battery bank — not the appliance's operating voltage — for an accurate result. Use the kWh → Ah tab above.

What is a derating or efficiency factor, and when should I use one?

A derating factor is a multiplier, typically between 0.75 and 1.0, that adjusts a theoretical energy calculation to reflect real-world conditions such as high ambient temperature, poor ventilation, motor efficiency losses, or aging equipment. Applying one gives a more conservative, realistic estimate than assuming ideal laboratory conditions. Leave it at 1.0 for the raw, unadjusted calculation, or pick one of the presets on the Watts → kWh tab.

How do I estimate electricity cost from kWh?

Multiply your total kWh by your electricity rate in dollars per kWh: Cost = kWh × Rate. Use the effective rate from your utility bill for the most accurate estimate — the optional Rate field on the Watts → kWh tab does this automatically. For comparing costs across several appliances at once, use the Electrical Cost Calculator instead.

What is the difference between kW and kWh?

kW (kilowatt) measures power — the rate energy is used at any given instant. kWh (kilowatt-hour) measures energy — the total amount used over a period of time. A 2 kW appliance running for 3 hours consumes 6 kWh, regardless of how the load varies during that time. If you need to convert kW directly to horsepower instead, see the kW to HP Converter.

How do I convert kWh back to average watts?

Multiply the kWh total by 1,000 and divide by the number of hours the energy was used over: Average Watts = (kWh × 1,000) ÷ Hours. This gives an average draw, not the instantaneous peak, which is useful when only a metered energy total and a time window are known. Use the kWh → Watts tab above.