Watts vs. kilowatt-hours: a practical explanation
Learn how electrical power becomes energy use and how to estimate kWh from everyday appliances.
Read the guide →A clearer view of home energy
Know what your electricity use really costs.
WattWise Lab turns appliance ratings, daily routines, and your local electricity price into practical estimates you can inspect and adjust.
No sign-up. No data entry is sent to our server by these calculators; calculations run in your browser.
A simple starting point
kWh × rate
Your estimated energy charge is the energy used in kilowatt-hours multiplied by your price per kWh. Fixed fees and taxes may be separate.
Example: 500 W × 4 hours ÷ 1,000 = 2 kWh per day.
Read the plain-English explanation →Free interactive tools
Useful calculators, built around real inputs
Each tool explains its formula, makes assumptions visible, and lets you change the inputs instead of hiding the calculation behind a score.
Electricity Cost Calculator
Estimate daily, monthly, and yearly kWh and cost from wattage and runtime.
Open calculator →Home Energy Planner
List multiple devices and identify the largest estimated contributors to your bill.
Open calculator →Air Conditioner Cost Estimator
Model cycling with an adjustable running fraction instead of assuming full load.
Open calculator →LED Lighting Savings
Compare bulb wattages, annual savings, and a simple upfront-cost payback.
Open calculator →Standby Power Cost
Estimate the cost of devices left in sleep or standby modes.
Open calculator →Solar Savings & Payback
Separate direct self-use from exported solar generation.
Open calculator →Compare Appliances
Compare monthly and yearly running cost between two devices.
Open calculator →Time-of-Use Electricity Cost Calculator
Estimate peak and off-peak charges from your tariff and billing period.
Open calculator →Field notes
Understand the numbers before acting on them
Our guides explain common rating-label confusion, appliance cycling, and the limits of estimates so you can make a better-informed comparison.
How to read appliance power labels
Find the right input value and avoid mixing electrical watts with output capacity.
Read the guide →Why air-conditioner costs are hard to estimate
Understand compressor cycling, weather, insulation, and realistic usage assumptions.
Read the guide →How to compare LED bulb replacements
Compare wattage, lumens, usage, and upfront cost without relying on a single marketing claim.
Read the guide →How to check standby electricity use
Identify which idle devices matter and how to measure them safely.
Read the guide →Solar self-consumption and payback basics
Understand the difference between using solar directly and exporting surplus energy.
Read the guide →How to Understand an Electricity Bill: Energy, Rates, and Extra Charges
Learn how to read kWh, unit prices, fixed charges, taxes, time-of-use periods, and adjustments on a household bill.
Read the guide →How to Estimate Refrigerator Electricity Use More Reliably
Use annual kWh labels, appropriate meter readings, and realistic operating conditions instead of assuming continuous compressor power.
Read the guide →A Practical Home Energy Audit Checklist You Can Complete in a Week
Use a seven-day checklist to record bills, identify major loads, review operating schedules, and prioritize safe, evidence-based improvements.
Read the guide →Our approach
Transparent estimates—not fake precision
Household electricity costs depend on more than a device's headline wattage. Runtime, operating mode, local tariff, and equipment cycling can change the result. WattWise Lab keeps those inputs visible so you can understand exactly what an estimate includes.
What these tools are designed to do
- Convert power and runtime into estimated kilowatt-hours.
- Apply an electricity rate that you provide instead of assuming one global price.
- Show the formula and limitations alongside the result.
- Help compare scenarios without claiming to predict your exact utility bill.
What they cannot know automatically
The tools do not retrieve your bill, inspect your appliances, identify your tariff, or verify your roof's solar potential. You supply the assumptions. For bills with tiered rates, taxes, fixed charges, time-of-use pricing, or export-credit rules, the calculation is a planning estimate rather than an exact invoice.
Read our editorial policy to see how we present formulas and corrections, and our disclaimer before using estimates for a major purchase.