Series and Parallel Resistance Calculator

This Series and Parallel Resistance Calculator works out the total resistance of up to four resistors connected either in series or in parallel, which is one of the most common tasks in electronics and physics study. You enter the resistance of each resistor in ohms and choose the configuration, and the tool returns the combined resistance of the network. The rules are simple but easy to mix up. In a series circuit the same current flows through every resistor, so the resistances simply add together and the total is always larger than the biggest single resistor. In a parallel circuit the voltage across each resistor is the same, the current splits between the branches, and you add the reciprocals of each resistance then take the reciprocal of that sum, so the total is always smaller than the smallest single resistor. Students, hobbyists, electricians and engineers use this to size resistor networks, set voltage dividers, plan current limiting and check circuit designs before building them. A few tips keep your answers trustworthy. Leave any unused resistor inputs at zero in series mode, since adding zero changes nothing, and avoid entering zero in parallel mode because a zero ohm branch is a short circuit and makes the maths blow up. Keep your units consistent, converting kilohms and megohms to ohms first, and remember that real resistors carry a tolerance, often 1 or 5 percent, so the measured value can differ from the nominal value you typed. Used this way the calculator gives a quick, dependable check that matches what your multimeter should read across the network.

Series total = R1 + R2 + R3 + R4. Parallel total = 1 / (1/R1 + 1/R2 + 1/R3 + 1/R4).