Electricity cost calculator

Estimate energy use and cost from entered power, usage time and rate.

Your inputs stay in your browser.

Method and assumptions

Method version 1.0.0 · Updated October 2, 2026

Calculate cost

Formula: Energy (kWh) = power (W) × hours × days ÷ 1,000.

The monetary result uses the currency of your rate.

powerWatts: Power (W)
hoursPerDay: Hours used per day
days: Number of days
pricePerKwh: Price per kWh

Power is assumed constant throughout the usage period. The entered rate is applied to all energy; standing charges, taxes and time-of-use pricing are excluded.

Calculate with code

These short examples use the same inputs and core calculation as this tool. Adapt validation and formatting to your application.

JavaScript

const watts = 1000, hoursPerDay = 3, days = 30, pricePerKwh = 0.25;
const kwh = watts * hoursPerDay * days / 1000;
console.log(kwh, kwh * pricePerKwh); // 90 kWh, 22.50

TypeScript

const watts = 1000, hoursPerDay = 3, days = 30, pricePerKwh = 0.25;
const kwh = watts * hoursPerDay * days / 1000;
console.log(kwh, kwh * pricePerKwh); // 90 kWh, 22.50

Python

kwh = 1000 * 3 * 30 / 1000
print(kwh, kwh * 0.25)  # 90.0 kWh, 22.5

Java

double kwh = 1000 * 3 * 30 / 1000.0;
System.out.println(kwh + " kWh, cost=" + kwh * 0.25); // 90.0, 22.5

decimal kwh = 1000m * 3 * 30 / 1000;
Console.WriteLine($"{kwh} kWh, cost={kwh * 0.25m}"); // 90, 22.50