Calculate your appliance energy usage and estimated costs.
Calculation Results:
Daily Consumption:0 kWh
Total Consumption:0 kWh
Estimated Cost:$0.00
How to Calculate Kilowatt Hours (kWh)
Understanding how to calculate kilowatt-hours is essential for managing home energy efficiency and predicting your monthly utility bills. A kilowatt-hour (kWh) is a unit of energy representing the amount of power consumed over a specific period.
The Standard kWh Formula
To find the kWh for any electrical appliance, you need to know its power rating (in Watts) and the duration for which it is used. The formula is as follows:
kWh = (Watts × Hours) / 1,000
Step-by-Step Calculation Guide
Find the Wattage: Look for a label on the back or bottom of your appliance. It will usually state the maximum power consumption in Watts (W).
Estimate Usage Time: Determine how many hours per day the device is actively running.
Convert to Kilowatts: Since there are 1,000 Watts in 1 Kilowatt, divide your total Watt-hours by 1,000.
Calculate Cost: Multiply the total kWh by your local utility company's rate per kWh.
Practical Example
Suppose you have a 100-Watt television that you watch for 4 hours every day. Here is how you calculate the monthly usage (30 days):
Monthly kWh: 0.4 kWh × 30 days = 12 kWh per month.
Monthly Cost: If your rate is $0.15 per kWh, your cost is 12 × 0.15 = $1.80.
Why Monitoring kWh Matters
By calculating the energy use of individual appliances, you can identify "energy vampires"—devices that consume significant power even when you aren't actively using them. High-wattage appliances like space heaters, air conditioners, and water heaters are typically the primary contributors to high electricity bills.
function calculateKWH() {
// Get input values
var watts = parseFloat(document.getElementById('applianceWattage').value);
var hours = parseFloat(document.getElementById('hoursPerDay').value);
var days = parseFloat(document.getElementById('daysUsed').value);
var rate = parseFloat(document.getElementById('costPerKwh').value);
// Validation
if (isNaN(watts) || isNaN(hours) || isNaN(days) || watts <= 0 || hours <= 0 || days <= 0) {
alert("Please enter valid positive numbers for Wattage, Hours, and Days.");
return;
}
// Default rate to 0 if not provided
if (isNaN(rate)) {
rate = 0;
}
// Calculation Logic
// Daily kWh = (Watts * Hours) / 1000
var dailyKwhValue = (watts * hours) / 1000;
// Total kWh = Daily kWh * Number of Days
var totalKwhValue = dailyKwhValue * days;
// Total Cost = Total kWh * Rate
var totalCostValue = totalKwhValue * rate;
// Display Results
document.getElementById('dailyKwh').innerText = dailyKwhValue.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 3}) + " kWh";
document.getElementById('totalKwh').innerText = totalKwhValue.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2}) + " kWh";
document.getElementById('totalCost').innerText = "$" + totalCostValue.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
// Show result area
document.getElementById('kwhResultArea').style.display = 'block';
}