Resistor Parallel / Series Calculator

How to use

1. 1Pick Parallel or Series at the top to match how your resistors are connected.
2. 2Add a row for each resistor. Type the value, choose the unit (mΩ, Ω, kΩ, MΩ), and set the tolerance percentage if you want a combined error band.
3. 3Use the quick presets to load a worked example (two 10kΩ in parallel, voltage divider, LED limiter, equal parallel set) and verify the math against a known answer.
4. 4Read the total resistance at the top of the output panel. The value is shown in the most natural unit, in exact ohms, and in every unit at once.
5. 5Optionally apply a voltage or current source to see per-resistor voltage drop, branch current, and power dissipation so you can pick the right resistor wattage rating.
6. 6Use the copy buttons to grab the total in ohms, a short form, or a full summary that includes the per-resistor breakdown.

About this tool

Resistor Parallel / Series Calculator computes the total resistance of any number of resistors connected in parallel or in series, the current flowing through each branch when a voltage or current source is applied, the voltage drop across each resistor, and the power each resistor dissipates so you can match the wattage rating you actually need. Series mode adds every resistor end to end so the total is the sum and every resistor shares the same current; parallel mode connects every resistor across the same two nodes so each branch sees the same voltage and the total is the reciprocal of the sum of conductances. Each row accepts a value in milliohms, ohms, kilohms, or megaohms, an optional tolerance percentage (1%, 5%, 10%, or any value you read off a color band), and a remove button when you want to thin out the network. Up to twenty resistors can be added at once, which is enough for most real circuits including pull-up networks, ladder dividers, current-sense banks, snubbers, and matched audio attenuators. The output panel reports the total in the most natural unit (a 5kΩ total is shown as 5 kΩ, not 5000 Ω), a precise exact value in ohms for reference, the formula being evaluated so you can verify the math, the total in every unit at once for cross-checking with other tools, and a combined tolerance band that uses additive deltas in series and a conductance-weighted first-order worst case in parallel. When a voltage or current source is configured, a per-resistor table appears with the voltage across each resistor, the current through it, and the power it dissipates, plus the total current and total power for the network as a whole. Quick presets cover the most common worked examples in electronics textbooks and real circuits (two 10kΩ in parallel, the classic 1kΩ + 2kΩ voltage divider, a 330Ω LED limiter, three 1kΩ in parallel, a 10k + 4.7k + 2.2k stack, and an asymmetric 100Ω + 1kΩ parallel pair) so you can sanity check the tool against textbook answers. A reference panel shows the formulas at a glance, including the product-over-sum shortcut for exactly two resistors in parallel and the divide-by-N shortcut for equal resistors in parallel. Useful for electronics hobbyists building one-off circuits on a breadboard, EE students working through homework problems, makers picking through a parts drawer to hit a target resistance, embedded engineers sizing pull-ups and current-limit resistors, audio enthusiasts tuning attenuators, and anyone wiring up an LED, a sensor divider, or a power rail and asking what total resistance these resistors give. Everything runs locally in your browser. Resistor values, voltages, and currents never leave your device.

Free to use. Works in your browser. No signup, no login.