What is the formula used?

Current is calculated as I = V / R (Ohm's Law). Power is P = V² / R (watts). Energy is E = P × t / 1000 (kilowatt-hours), where t is time in hours.

Why divide by 1000 to get kWh?

Kilowatt-hours use kilowatts, not watts. Since 1 kW = 1000 W, dividing watt-hours by 1000 gives kilowatt-hours.

Does this work for AC and DC circuits?

This calculator assumes a purely resistive load with constant voltage, which is a valid approximation for both DC and purely resistive AC loads (heaters, incandescent bulbs). For inductive or capacitive loads, impedance rather than pure resistance should be used.

How do I find the resistance of my device?

Use a multimeter set to ohms mode with the device unplugged. You can also calculate it from the device's rated wattage and voltage: R = V² / P.

How do I estimate electricity cost from kWh?

Multiply the kWh result by your electricity rate (e.g., $0.12 per kWh). The calculator shows this automatically when you enter a rate.

Ohms to Kilowatt Hours Calculator

Name: Ohms to Kilowatt Hours Calculator
Availability: InStock
Author: Nham Vu

Enter resistance (ohms), voltage (V), and time (hours) to calculate energy consumption in kilowatt-hours.

Input Values

Resistance (Ω)

Resistance of the load in ohms

Voltage (V)

Supply voltage in volts

Time (hours)

Duration the device is running

Electricity Rate ($/kWh) — optional

Your electricity cost per kWh for cost estimate

Enter values and click Calculate to see results

Summary

Enter resistance (ohms), voltage (V), and time (hours) to calculate energy consumption in kilowatt-hours.

How it works

Enter the resistance of your device in ohms (Ω).
Enter the supply voltage in volts (V).
Enter the duration the device runs in hours.
The calculator derives current using Ohm's Law: I = V / R.
Power is computed as P = V² / R, then energy as E = P × t / 1000.
Results show power in watts and energy in kilowatt-hours (kWh).

Use cases

Estimate electricity consumption for electric heaters and heating elements.
Calculate energy cost for resistive loads in industrial equipment.
Check power draw of a known resistance at a given voltage.
Verify energy usage for DIY electronics projects.
Compare energy consumption across different operating voltages.
Estimate monthly electricity bills for appliances with known resistance.

Frequently Asked Questions

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Last updated: 2026-05-23 · Reviewed by Nham Vu