Current Sense (Shunt) Resistor Calculator
Size a shunt resistor and check its power dissipation for a current-sense circuit.
Sizing a current-sense (shunt) resistor
A shunt resistor converts current into a measurable voltage: Vsense = I × Rsense. Pick Rsense so your full-scale current produces a full-scale sense voltage that matches your amplifier or ADC's useful input range — Rsense = Vfs / Imax. Common full-scale targets are 50–100 mV: high enough to stay well above the amplifier's input offset voltage (so offset error doesn't dominate at low currents), low enough that the resistor doesn't waste significant power or disturb the circuit it's measuring.
Power dissipation sets the resistor's required power rating: worst case at Imax, P = Imax² × Rsense. Since sense resistors usually run continuously rather than at full scale, the more useful number for thermal/efficiency budgeting is the dissipation at typical operating current, Ptyp = Ityp² × Rsense — that's the number to compare against your power budget, while the full-scale figure sets the minimum power rating (with the usual 2× derating margin) so the part survives worst-case transients.
Trade-offs: a bigger Rsense gives a stronger signal (better SNR, less amplifier offset error) but burns more power and adds more series resistance, which drops the supply/load voltage and matters more as Imax grows. This is why low-side, low-value shunt sensing (with a precision current-sense amplifier) dominates in power electronics — the resistor stays a few mΩ to tens of mΩ, and the gain comes from the amplifier instead of the resistor.