Resistors in Parallel Calculator

The answer is always below the smallest resistor

Adding another path can only make current flow more easily, never less. Two equal resistors in parallel give exactly half their value; 100 Ω beside 1 MΩ gives 99.99 Ω, because almost nothing goes through the large one. If your result exceeds the smallest resistor, the arithmetic is wrong — which is why that figure is shown next to the answer.

What this page needs from you

This page asks for r1 in Ω, r2 in Ω and r3 (0 to skip) in Ω. From those it returns total resistance in Ω, together with smallest resistor for comparison, current at 12 v, two equal resistors would give and total conductance. Every figure updates as you type, and nothing you enter leaves your browser.

Check the power rating, not just the value

Choosing a component by its resistance or capacitance alone leaves out the rating that actually determines whether it survives. Work out the power the part will dissipate and pick something rated for at least twice it: a resistor run at its limit gets hot enough to drift out of tolerance and to discolour the board.