How is electricity cost per kWh calculated?

Energy in kilowatt-hours equals watts divided by 1000 times hours of use. Multiply that by your rate per kWh to get the cost. Daily energy is scaled by 30.44 days for a month and 365.25 days for a year.

What is a kilowatt-hour?

A kilowatt-hour is the energy used by a 1000-watt load running for one hour. A 1500-watt heater run for four hours uses 6 kWh, which is what your utility bills you for.

How do two-tier rates work?

Many utilities charge a lower rate up to a monthly kWh threshold, then a higher rate above it. The calculator splits your monthly consumption across the limit, prices each portion at its rate, and reports the blended effective cost per kWh.

Why use 30.44 days for a month?

Using the average number of days per month (365.25 divided by 12) keeps the monthly figure consistent with the annual one, avoiding the rounding error that a flat 30 or 31 days would introduce.

Does this include standing charges or taxes?

No. The result reflects only the energy cost of the load at the per-kWh rate you enter. Fixed daily standing charges, connection fees and taxes are billed separately and should be added to estimate a full bill.

What is the Electricity Cost Calculator?

Enter appliance wattage, hours of use per day and your utility rate per kWh to compute hourly, daily, monthly and annual energy cost and consumption. Supports two-tier rate structures to model the cost of any specific electrical load. It runs free in your browser on Gera Tools, with nothing uploaded.

Electricity Cost Calculator

Name: Electricity Cost Calculator
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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Knowing the running cost of a specific appliance or circuit makes it easy to decide whether to upgrade, time-shift or switch off a load. This calculator turns wattage, hours of use and your utility rate into hourly, daily, monthly and annual cost, and can model a two-tier tariff where the price steps up after a monthly threshold.

Common appliance wattages for reference

If you are not sure of an appliance’s wattage, check the nameplate label (usually on the back or bottom). As a general reference:

Appliance	Typical wattage
LED bulb	8–15 W
Laptop	45–65 W
Desktop PC (idle)	60–100 W
TV (50”, LCD)	70–120 W
Refrigerator	100–200 W (running draw)
Washing machine	400–1,500 W
Electric kettle	1,200–1,800 W
Space heater	750–1,500 W
Air conditioner (window unit)	900–1,500 W
Electric oven	2,000–5,000 W

These are typical running wattages, not peak or startup wattage. For appliances that cycle (refrigerators, AC), use the average running draw rather than the compressor peak.

How it works

The core formula converts power and time into energy, then prices it:

kWh/day  = watts / 1000 × hours/day
cost/day = kWh/day × rate

Monthly and annual figures use average calendar lengths (30.44 and 365.25 days) so they stay consistent with each other. When two-tier pricing is enabled, the monthly kWh is split at the threshold:

cost/month = min(kWh, limit) × rate1 + max(0, kWh − limit) × rate2

The tool reports the resulting blended effective rate so you can see what you are actually paying per kWh on average.

Worked examples

Example 1 — space heater: A 1,500 W space heater run 4 hours a day at $0.17/kWh:

kWh/day   = 1,500 / 1,000 × 4 = 6 kWh
cost/day  = 6 × 0.17         = $1.02
cost/month = 6 × 30.44 × 0.17 ≈ $31.05
cost/year  = 6 × 365.25 × 0.17 ≈ $372.55

Example 2 — LED vs incandescent comparison: An old 60 W incandescent and a 9 W LED, each on 5 hours/day at $0.20/kWh:

Incandescent: 0.06 × 5 × 365.25 × 0.20 ≈ $21.91/year
LED:          0.009 × 5 × 365.25 × 0.20 ≈ $3.29/year
Annual saving: ≈ $18.62 per bulb

Example 3 — two-tier tariff: You use 400 kWh/month on a tariff with rate1 = $0.12 below 300 kWh and rate2 = $0.22 above:

First 300 kWh × $0.12 = $36.00
Next 100 kWh × $0.22  = $22.00
Total                   = $58.00
Blended rate            = $58.00 / 400 = $0.145/kWh

Tips for more accurate estimates

Use measured wattage if possible. A plug-in energy monitor (smart plug with energy measurement) gives the real average draw, especially for cycling appliances.
The nameplate is the maximum. Appliances rarely run at their rated wattage continuously; actual draw is typically lower.
Standing charges are separate. Most utility bills include a fixed daily or monthly standing charge on top of the per-kWh energy charge. This tool models only the energy cost.