Energy Consumption Calculator

What This Calculator Does

Enter an appliance’s wattage and how many hours per day you use it. The calculator converts those two values into kilowatt-hours (kWh) — the universal unit for measuring electrical energy — and shows your daily, monthly (× 30), and annual (× 365) consumption.

This calculator measures energy use only. It does not calculate electricity cost. To estimate your bill, take the kWh result from this page to the Electricity Cost Calculator and enter your tariff rate.

How kWh Is Calculated

Formula:
kWh = (Watts × Hours per day) ÷ 1,000

Dividing by 1,000 converts watts (W) to kilowatts (kW). Multiplying by hours gives the energy used in kilowatt-hours. This is the figure your electricity meter records and your provider bills.

Unit note: kW is a rate (power at any instant); kWh is a quantity (energy accumulated over time). A 1,000 W appliance running for 1 hour uses exactly 1 kWh. Running it for 30 minutes uses 0.5 kWh.

Worked Examples

Example 1 — 65-inch LED TV (100 W, 5 h/day):
(100 × 5) ÷ 1,000 = 0.5 kWh/day → 15 kWh/month → 182.5 kWh/year
A relatively low-consumption device. Running it 8 h/day raises annual use to 292 kWh.

Example 2 — Refrigerator (150 W rated, cycling):
Enter 70 W (approx. 47% duty cycle): (70 × 24) ÷ 1,000 = 1.68 kWh/day → 613 kWh/year
Fridges run 24 h/day but cycle on/off. Using rated wattage (150 W) overestimates by ~2×. Check your energy label for the actual annual kWh figure if available.

Example 3 — 2,500 W electric space heater (6 h/day):
(2,500 × 6) ÷ 1,000 = 15 kWh/day → 450 kWh/month
High-wattage appliances dominate energy consumption. A single space heater can account for more kWh per month than all other appliances combined.

How to Reduce Energy Consumption

• Reduce daily usage time — cutting hours has a direct linear effect on kWh consumed
• Switch to energy-efficient alternatives — LED bulbs use 80% less energy than incandescent; inverter ACs use 30–50% less than fixed-speed models
• Eliminate standby draw — devices left in standby still consume 0.5–5 W continuously; unplug or use switched sockets
• Focus on high-wattage appliances first — heaters, dryers, air conditioners, and EV chargers account for the majority of household kWh

Energy Consumption vs Electricity Cost

These are two separate calculations:

• Energy consumption (this page): how many kWh a device uses. Output is in kWh — no currency involved.
• Electricity Cost Calculator: multiplies kWh by your tariff rate to produce a cost figure in your currency. Use that page to estimate your bill.

Use this page first to understand usage; then use the cost calculator to convert kWh into money. For a breakdown by specific appliance type with auto-filled wattage presets and cost output in one step, the Appliance Electricity Cost Calculator combines both calculations on a single page.

Common Mistakes

• Using rated wattage for cycling appliances: refrigerators, ACs, and washing machines cycle on and off. Their nameplate wattage is the peak draw, not the average. For these, use a lower effective wattage or read the annual kWh from the EU/UK energy label directly.
• Entering kW instead of W: if the label says “2.5 kW”, enter 2500. Entering 2.5 gives a result 1,000× too low.
• Not accounting for standby power: a device plugged in but “off” often still draws 0.5–5 W. For devices left plugged in all day, add a separate calculation using standby wattage × 24 h.

Important Limitations

• Assumes constant wattage: the calculator multiplies a fixed watt value by hours. Devices with variable power draw (laptops under load vs idle, dimmed lights, variable-speed motors) consume unevenly — results are estimates.
• No standby or inrush capture: start-up current surges and standby drain are not included unless you add them as separate calculations.
• No efficiency losses: EV chargers, inverters, and battery chargers lose 5–15% to heat. The kWh drawn from the wall is higher than the energy stored or delivered.