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Ohm’s law Calculator

Calculate current and power in a resistive circuit.

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How to use this calculator

Your measurements

Enter your project values to update the estimate.

Item name (optional)

View your estimate

Assumes a constant resistance and voltage. Installation design and protective devices require separate assessment.

YOUR ESTIMATE

Current

Power24 W

Calculated from your measurements.

PLAN YOUR PROJECT COST

Pricing calculator

Use your supplier’s rate or enter a quoted total. Save each estimate to your project and print everything together.

What are you pricing?

Price is per

Price (optional)

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Your selected quantity already includes any allowance shown in that result. Check whether you are pricing individual items or whole packs. Delivery, tax and labour are not added automatically. A quoted total applies only to this saved calculation.

Ohm’s law Calculator: measuring notes and method

Use the voltage across the resistance

The entered voltage must be across the particular resistance being calculated. A supply voltage may be shared between components, so it is not automatically the voltage across each one.

Check component conditions

Resistance can change with temperature, and calculated dissipation is not a component power-rating recommendation. This simple model does not handle reactive AC impedance.

Formula

Current = voltage ÷ resistance. Power = voltage² ÷ resistance.

Product reference: Fluke electrical glossary

Worked example

Illustrative values match Reset example and stay fixed when you edit the calculator.

Starting-value worked example

Voltage: 12 V
Resistance: 6 Ω

Current: 2 A

Follow the calculation

Current = 12 ÷ 6 = 2 A.
Power = 12² ÷ 6 = 24 W.

Reviewed 19 October 2026. How calculations are checked · Report a correction

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Electrical power CalculatorCalculate power from voltage and current.Current from power CalculatorCalculate current for a known power and voltage.Energy use CalculatorEstimate energy consumption from power and running time.Material cost CalculatorEstimate material cost with an optional contingency.

PRACTICAL READING

Understand the inputs. Check the order.

Measurement methods and worked examples to use alongside this calculator.

Know when simple volts, amps and watts formulas applyUse the electrical tools as arithmetic checks with explicit circuit assumptions.
Measure energy use and cable routes as separate planning tasksOperating time determines energy; a measured route determines cable quantity.
Check units before multiplying measurementsAvoid the square and cubic conversion mistakes that can make a plausible-looking estimate wrong.
Build a measurement register you can check laterRecord where each number came from before it becomes part of a material order.

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