Shunt Resistor Calculator

Work out shunt resistor instantly with clear inputs, formula shown and shareable results.

About Shunt Resistor Calculator

A current shunt is a precise low-value resistor: R = full-scale voltage divided by full-scale current, so a 50 A / 75 mV shunt is 1.5 milliohms. Dissipation at full scale is I squared R, which is why high-current shunts need substantial physical size and often forced cooling.

Formula

Shunt resistor

R = Vfs / Ifs; P = I^2 x R; measured voltage = I x R

Worked example

With the default values below, Shunt Resistor Calculator returns Shunt resistance of 1.5000. Change any input above and every figure here is recalculated in your browser.

Inputs used

Full-scale current: 50 A
Shunt voltage at full scale: 75 mV
Current being measured: 32 A

Results

Shunt resistance: 1.5000 mΩ
Power dissipated at full scale: 3.75 W
Shunt output at the measured current: 48.00 mV
Power at the measured current: 1.54 W

Step by step

1Values used
2Shunt resistor
3Shunt resistance= 1.5000 mΩ
4Power dissipated at full scale= 3.75 W
5Shunt output at the measured current= 48.00 mV
6Power at the measured current= 1.54 W

Assumptions and limits

The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
Electrical results are planning estimates only. Verify against the applicable wiring rules (IEC 60364, BS 7671, NEC or local code) and have all installation work designed and checked by a qualified electrician.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Electrical results are planning estimates only. Verify against the applicable wiring rules (IEC 60364, BS 7671, NEC or local code) and have all installation work designed and checked by a qualified electrician.

Frequently Asked Questions

Why is 75 mV a standard?

Panel meters and analogue instruments were standardised on 50, 75 or 100 mV full scale, so shunts are still made to match. It is a compromise between signal size and dissipation.

Why use four-terminal shunts?

Separate sense terminals keep the lead and contact resistance out of the measurement, which matters enormously when the shunt itself is only a milliohm.