Electricity Calculator
Adjust the inputs below. Results update as you type.
How it works
Ohm's law: V = IR. Watt's law: P = VI = I²R = V²/R. For AC circuits, apparent power (VA) differs from real power (W) by the power factor (PF = cos φ). Enter any two of the four values and the others are solved. Used in circuit design, electrical troubleshooting, and understanding energy consumption of household appliances.
Input guidance
- Confirm date/time/unit settings before comparing outputs.
- If a task has optional fields, run both with and without them to understand impact.
- Save scenario variants when making practical decisions.
The formula
Energy = power (kW) × time (hours). Cost = energy (kWh) × price per kWh. A device's kW is its watt rating ÷ 1000.
Worked example
A 1,500-watt heater for 5 hours uses 1.5 × 5 = 7.5 kWh; at $0.15/kWh that costs $1.13.
More examples to test
- Quick-pass example: run default assumptions for a first estimate.
- Refined example: update one assumption at a time to isolate impact.
How to interpret results
Use outputs as operational estimates and pair them with local constraints, business rules, or provider requirements.
When this can be inaccurate
Utilities can miss local policy details, special-case rules, and environment-specific constraints.
Change history
- July 2026: Quality-reviewed for publication with formula checks and explanatory copy updates.
Site-wide corrections also appear on the corrections log.
Find productivity tools for everyday workflows
General recommendation, not professional advice.
Frequently asked questions
What is a kilowatt-hour?+
The energy of using one kilowatt for one hour — the unit utilities bill by. A 100-watt bulb for 10 hours uses 1 kWh.
How do I find a device's running cost?+
Convert its watts to kilowatts, multiply by hours of use to get kWh, then multiply by your electricity rate.
Which appliances cost the most?+
Heating and cooling, water heaters, and electric dryers draw the most power, so small efficiency gains there save the most money.
Why are outputs slightly different from another tool?+
Different tools can use different rounding rules, default assumptions, and treatment of edge cases.
How can I improve estimate reliability?+
Use verified inputs from real records and re-run calculations after major assumption changes.
Guided next steps
Want the full workflow? Use this calculator inside a step-by-step guide.