How do you calculate resistors in parallel?

Add the reciprocals of every resistance and take the reciprocal of the result: 1/Rtotal = 1/R1 + 1/R2 + … + 1/Rn. For exactly two resistors the shortcut Rtotal = (R1 × R2) / (R1 + R2) gives the same answer. This calculator applies the formula to as many resistors as you enter.

What is the total resistance of two 10 kΩ resistors in parallel?

5 kΩ. Identical resistors in parallel divide evenly, so n equal resistors of value R give R/n — two 10 kΩ resistors give 5 kΩ, three give 3.33 kΩ, and so on.

Why is parallel resistance always lower than the smallest resistor?

Each parallel branch adds another path for current. More paths means more total current for the same voltage, and by Ohm’s law more current at a fixed voltage means less resistance. The total therefore always lands below the smallest single resistor in the group.

Can this calculator do resistors in series too?

Yes. Switch the Connection setting from Parallel to Series and the same resistor list is summed instead: Rtotal = R1 + R2 + … + Rn.

Does it account for resistor tolerance, voltage, and power ratings?

Yes. Enable the Tolerance, Voltage, or Power options and each resistor can carry its own ratings. The results table then reports the combined tolerance and the voltage and wattage ratings of the network, each with worst-case minimum and maximum bounds alongside the nominal value.

Do I need an account to use it?

No. The parallel resistor calculator is free and stateless, with generous daily limits and no registration required.

Parallel Resistor Calculator — Total Resistance of Resistors in Parallel

Combine any number of resistors in parallel or in series, with optional tolerance, voltage, and power ratings

What Is Parallel Resistance?

Resistors are in parallel when both ends of each resistor connect to the same two nodes, so every resistor sees the same voltage and the current splits between them. Because each extra resistor opens another path for current to flow, the network as a whole conducts more easily than any single branch — which is why the total resistance always comes out lower than the smallest resistor in the group.

Series is the opposite arrangement: resistors sit end to end in a single chain, the same current passes through all of them, and the resistances simply add up. This calculator handles both — pick the connection type and enter as many resistors as you need.

The Parallel Resistance Formula

The general formula sums the reciprocals of every resistance and then takes the reciprocal of the result:

1/R_total = 1/R₁ + 1/R₂ + … + 1/R_n

For exactly two resistors the “product over sum” shortcut is easier to do in your head and gives an identical answer:

R_total = (R₁ × R₂) / (R₁ + R₂)

A useful special case: n identical resistors of value R in parallel give R/n. Two 10 kΩ resistors give 5 kΩ, four 1 MΩ resistors give 250 kΩ. This is the standard trick for reaching a value you do not stock, and for splitting power dissipation across several parts. For a series connection the formula is simply R_total = R₁ + R₂ + … + R_n.

How to Use the Parallel Resistor Calculator

Choose the connection type. Select Parallel or Series in the Settings panel. Every resistor in the list is combined using the formula for that connection.
Add your resistors. Use the Add Resistor button to create a row for each part and enter its resistance. The unit selector next to each field switches between μΩ, mΩ, Ω, kΩ, and MΩ, so you can mix units freely in the same calculation.
Turn on the ratings you care about. The Tolerance, Voltage, and Power switches add those fields to each resistor and add matching rows to the results.
Set the rounding. Pick between 1 and 6 decimal places for the output.
Calculate. The results table reports the total resistance and, where enabled, the combined tolerance and the voltage and wattage ratings of the network — each with worst-case minimum and maximum bounds next to the nominal value.

Why Tolerance Matters in a Parallel Network

Real resistors are not their marked value. A 10 kΩ ±5 % part is somewhere between 9.5 kΩ and 10.5 kΩ, and when several such parts are combined those errors stack. Enabling the Tolerance option shows the worst-case spread of the finished network, which is what you actually need when the value feeds a reference, a divider, or a current-sense circuit. Voltage and power ratings are worth checking too: in a parallel network the same voltage appears across every resistor, so the branch with the lowest voltage rating limits the whole group.

When to Use a Different Resistora Tool

This page combines a flat list of resistors that are all in parallel, or all in series. If your circuit mixes the two — a series resistor feeding a parallel pair, for example — use the circuit resistance calculator, which builds the network from 16 series/parallel topologies and analyses it as a whole.

If you are working the other way round — you know the resistance you want and need to know which parts to wire together to get it — use the resistor combination finder, which searches the resistors you own for the closest buildable match, or the E-series resistor finder to hit the target using standard E6–E192 values you can buy.

Plan Limits

The calculator is free to use without an account: anonymous visitors get 50 calculations a day, and a free account raises that to 100 a day. PRO accounts get 1,000 a day with no monthly cap, plus REST API and MCP access to the same calculation.

Related Tools

Voltage Divider Finder

Combining resistors to scale a voltage rather than just add resistance? Search for a divider pair instead.

Voltage Divider Builder

Already have a divider pair in mind? Plug the values in directly to get the exact output voltage.

E-Series Resistor Finder

Need resistors you can actually buy? Search standard E6–E192 catalog values for a target resistance.

Related Guides

How to Calculate Parallel Resistance

Want the derivation behind the reciprocal formula this calculator uses, plus the product-over-sum shortcut worked by hand?

Series vs Parallel Resistors — When to Use Which

Not sure whether your circuit calls for series or parallel? See how voltage and current behave in each before you pick a connection type above.

Frequently Asked Questions

How do you calculate resistors in parallel?: Add the reciprocals of every resistance and take the reciprocal of the result: 1/Rtotal = 1/R1 + 1/R2 + … + 1/Rn. For exactly two resistors the shortcut Rtotal = (R1 × R2) / (R1 + R2) gives the same answer. This calculator applies the formula to as many resistors as you enter.
What is the total resistance of two 10 kΩ resistors in parallel?: 5 kΩ. Identical resistors in parallel divide evenly, so n equal resistors of value R give R/n — two 10 kΩ resistors give 5 kΩ, three give 3.33 kΩ, and so on.
Why is parallel resistance always lower than the smallest resistor?: Each parallel branch adds another path for current. More paths means more total current for the same voltage, and by Ohm’s law more current at a fixed voltage means less resistance. The total therefore always lands below the smallest single resistor in the group.
Can this calculator do resistors in series too?: Yes. Switch the Connection setting from Parallel to Series and the same resistor list is summed instead: Rtotal = R1 + R2 + … + Rn.
Does it account for resistor tolerance, voltage, and power ratings?: Yes. Enable the Tolerance, Voltage, or Power options and each resistor can carry its own ratings. The results table then reports the combined tolerance and the voltage and wattage ratings of the network, each with worst-case minimum and maximum bounds alongside the nominal value.
Do I need an account to use it?: No. The parallel resistor calculator is free and stateless, with generous daily limits and no registration required.