Calculator inputs
Formula used
Ideal shunt resistance
Rsh = (Im × Rm) / (It − Im)
Burden voltage
V = Im × Rm
Shunt power
Psh = Ish² × Rsh
Temperature-adjusted resistance
R(T) = Rref × [1 + α × (T − Tref)]
- Rsh = shunt resistance.
- Im = meter full-scale current.
- Rm = meter internal resistance.
- It = target full-scale current.
- Ish = shunt current, which equals
It − Im. - α = temperature coefficient in per degree Celsius.
How to use this calculator
- Enter the meter full-scale current and choose its unit.
- Enter the meter internal resistance in ohms.
- Enter the desired maximum current and choose its unit.
- Set a power safety factor for practical resistor selection.
- Optionally include temperature values and material coefficient.
- Press the calculate button to show results above the form.
- Review resistance, voltage, current split, and wattage.
- Export the result table as CSV or PDF.
Example data table
| Meter full-scale current | Meter resistance | Target current | Shunt resistance | Burden voltage | Shunt power |
|---|---|---|---|---|---|
| 50 mA | 1 Ω | 5 A | 10.10101 mΩ | 50 mV | 247.5 mW |
| 1 mA | 100 Ω | 1 A | 100.1001 mΩ | 100 mV | 99.9 mW |
| 75 mA | 200 mΩ | 10 A | 1.511335 mΩ | 15 mV | 148.875 mW |
| 100 μA | 1 kΩ | 500 mA | 200.040008 mΩ | 100 mV | 49.99 mW |
These examples help compare common shunt sizing conditions quickly.
Frequently asked questions
1. What does a shunt resistor do?
A shunt resistor bypasses most current around a sensitive meter. The meter sees only its rated full-scale current, while the shunt safely carries the remaining current.
2. Why must target current exceed meter current?
The shunt is designed to divert extra current. If target current is not greater, no current bypass is needed and the shunt equation becomes invalid.
3. What is burden voltage?
Burden voltage is the voltage dropped across the meter and shunt combination at full scale. Lower burden usually improves efficiency and reduces circuit disturbance.
4. Why include a power safety factor?
Real resistors need thermal margin. A safety factor helps you choose a wattage rating that runs cooler, improves reliability, and tolerates overloads better.
5. Does temperature affect shunt accuracy?
Yes. Resistance changes with temperature. Low-TCR materials, such as manganin, reduce drift and keep current measurement more stable across operating conditions.
6. Can this calculator help with digital current sensing?
Yes. The same resistance, voltage drop, and power logic applies to many sensing designs. Still, amplifier offset, ADC range, and layout should also be checked.
7. What tolerance should I choose for the resistor?
Choose tolerance based on measurement accuracy goals. Precision current work often uses low-value, low-TCR shunts with 1%, 0.5%, or tighter tolerances.
8. Why are very low shunt values challenging?
Very low resistances are affected by lead resistance, solder joints, trace heating, and measurement error. Four-terminal shunts are often preferred for better accuracy.