Shunt Resistor Calculator — Resistance, Voltage Drop & Power
By Santaji GadepatilinUpdated October 30, 2026
A current shunt is a precise low-value resistor whose small voltage drop is proportional to the current through it. This shunt resistor calculator finds the resistance for a given full-scale current and millivolt rating, the drop and power at any current, and the reading you should expect — see shunt resistors in instrumentation, and Hall-effect current sensors for an isolated alternative.
How to use the shunt resistor calculator
Enter the shunt’s rated current and full-scale millivolt drop (from the nameplate, for example 50 A / 75 mV), and the current you are measuring. The calculator returns the shunt resistance, its power at full scale, and the voltage drop and power at your current. To design a current-sense resistor, enter the current and the drop your amplifier or ADC needs.
Shunt resistor formulas
R = VFS ÷ IFS · V = I × R · P = I² × R
Example
A 50 A / 75 mV DC shunt carrying 30 A:
- R = 0.075 ÷ 50 = 1.50 mΩ
- Voltage drop = 30 × 1.50 mΩ = 45 mV
- Power = 30² × 0.0015 = 1.35 W (full scale: 3.75 W)
Resistance and full-scale power of standard shunts
| Rated current | 75 mV shunt | Power at 75 mV | 50 mV shunt | Power at 50 mV |
|---|---|---|---|---|
| 5 A | 15 mΩ | 0.375 W | 10 mΩ | 0.25 W |
| 10 A | 7.5 mΩ | 0.75 W | 5 mΩ | 0.5 W |
| 20 A | 3.75 mΩ | 1.5 W | 2.5 mΩ | 1 W |
| 50 A | 1.5 mΩ | 3.75 W | 1 mΩ | 2.5 W |
| 100 A | 0.75 mΩ | 7.5 W | 0.5 mΩ | 5 W |
| 200 A | 0.375 mΩ | 15 W | 0.25 mΩ | 10 W |
| 500 A | 0.15 mΩ | 37.5 W | 0.1 mΩ | 25 W |
| 1000 A | 0.075 mΩ | 75 W | 0.05 mΩ | 50 W |
Notes
- Low-side shunts are easy to read but lift the load’s ground; high-side shunts need a current-sense amplifier with enough common-mode range.
- Manganin shunts have a very low temperature coefficient (about 15 ppm/°C), which keeps the reading stable as they warm.
- Check the ADC resolution against the small shunt signal with the ADC resolution calculator.
Frequently asked questions
How do I calculate shunt resistance?
R = full-scale voltage ÷ full-scale current. A 50 A, 75 mV shunt is 0.075 ÷ 50 = 1.5 mΩ.
How do I convert the shunt voltage back to current?
I = V ÷ R. On a 50 A / 75 mV shunt, every 1.5 mV is 1 A — a 45 mV reading means 30 A. Clear the current and enter the measured millivolts.
How much power does a shunt dissipate?
P = I² R = V × I. The 50 A / 75 mV shunt dissipates 3.75 W at full current. Many manufacturers rate shunts for continuous use at about two-thirds of nameplate current to limit heating and drift.
Why do shunts have four terminals?
The large terminals carry the current; the small sense screws measure the voltage across the calibrated section only (Kelvin connection), so contact and lead resistance do not add error.