Parallel Resistance Calculator
Calculate the equivalent resistance of resistors in parallel. Enter two or more resistor values in ohms to get the total resistance with the formula shown.
Updated 2026-06-14 · Free · No sign-up · Runs privately in your browser
Enter resistor values in ohms (Ω), separated by commas, spaces or new lines. Leave blank/zero entries out.
Show the formula & steps
How the Parallel Resistance Calculator Works
When resistors are connected in parallel, they share the same voltage but split the current, lowering the overall resistance. Enter two or more resistor values in ohms (Ω), separated by commas or spaces, and the calculator returns the equivalent resistance, the total conductance and the number of resistors counted.
The Formula
The equivalent resistance of any number of parallel resistors is found by summing reciprocals:
1 ÷ R_total = 1/R1 + 1/R2 + … + 1/Rn
For exactly two resistors there is a handy shortcut:
R_total = (R1 × R2) ÷ (R1 + R2)
Because conductance (1/R) adds in parallel, the result is always smaller than the smallest resistor in the set.
Worked Example
For three resistors of 100 Ω, 220 Ω and 330 Ω in parallel:
- 1 ÷ R_total = 1/100 + 1/220 + 1/330 = 0.01 + 0.004545 + 0.003030 = 0.017576 S
- R_total = 1 ÷ 0.017576 = ≈ 56.9 Ω
As expected, 56.9 Ω is below the smallest resistor (100 Ω).
Quick Reference for Equal Resistors
When all resistors share the same value R, the total is R divided by the count.
| Number of equal resistors | Each value | Equivalent resistance |
|---|---|---|
| 2 | 100 Ω | 50 Ω |
| 3 | 100 Ω | 33.3 Ω |
| 4 | 100 Ω | 25 Ω |
| 10 | 100 Ω | 10 Ω |
Series vs. Parallel
In a series circuit, resistances simply add and the total grows. In a parallel circuit, the reciprocals add and the total shrinks. If you are wiring components to lower resistance or to share current across multiple paths, parallel is the configuration you want, and this calculator gives the exact equivalent value.
Frequently asked questions
How do you calculate resistance in parallel?+
Add the reciprocals of every resistor, then take the reciprocal of that sum: 1 ÷ R_total = 1/R1 + 1/R2 + ... For two resistors you can use the shortcut R = (R1 × R2) ÷ (R1 + R2). The calculator handles any number of resistors at once.
Why is parallel resistance lower than each resistor?+
Adding a parallel path gives current another route to flow, which lowers the overall opposition. The equivalent resistance is always smaller than the smallest single resistor in the group, because more paths mean more total current for the same voltage.
What is the formula for two resistors in parallel?+
For exactly two resistors the product-over-sum shortcut is R = (R1 × R2) ÷ (R1 + R2). For example, 100 Ω and 220 Ω in parallel give (100 × 220) ÷ (100 + 220) = 22,000 ÷ 320 ≈ 68.75 Ω. The calculator shows this shortcut whenever you enter two values.
What happens with identical resistors in parallel?+
If all resistors are equal, the total is one resistor's value divided by the number of resistors. Two 100 Ω resistors in parallel give 50 Ω; three give 33.3 Ω; ten give 10 Ω. This is a quick mental check for matched resistors.
What is conductance?+
Conductance is the reciprocal of resistance, measured in siemens (S). In parallel, conductances simply add, which is why the formula sums 1/R terms. The calculator reports total conductance in millisiemens alongside the equivalent resistance.