Enter two or more resistors connected in parallel to calculate the equivalent resistance. Optionally add source voltage to estimate branch currents and total power.
Tip: Enter 0 Ω to model an ideal short branch. In that case, equivalent resistance becomes 0 Ω.
What this parallel resistor calculator does
This calculator finds the total resistance for resistors wired in parallel. In a parallel network, all branches share the same voltage, while current splits between branches. Because each added branch creates another path for current, total resistance always drops when you add a new resistor in parallel.
The tool supports:
- Any number of parallel resistors
- Decimal resistance values
- Optional supply voltage for current and power estimates
- Automatic handling of ideal short-circuit branches (0 Ω)
Formula used for equivalent resistance
For resistors in parallel, the reciprocal of total resistance is the sum of reciprocals:
1 / Req = 1 / R1 + 1 / R2 + ... + 1 / Rn
Rearranged:
Req = 1 / (1 / R1 + 1 / R2 + ... + 1 / Rn)
Special case: short branch
If any branch is 0 Ω, current has an ideal short path. That makes overall parallel resistance 0 Ω.
How to use this calculator
- Enter each resistor value in ohms (Ω).
- Click Add resistor if you need more branches.
- Optionally enter supply voltage to compute branch/total current.
- Set decimal precision.
- Click Calculate.
Worked examples
Example 1: Two resistors in parallel
Suppose you have 100 Ω and 200 Ω in parallel:
1 / Req = 1/100 + 1/200 = 0.015
Req = 1 / 0.015 = 66.6667 Ω
Example 2: Three equal resistors
Three 330 Ω resistors in parallel produce:
Req = 330 / 3 = 110 Ω
For equal resistor values, you can use a shortcut:
Req = R / n
Example 3: Add voltage to find current
If Req is 66.6667 Ω and source voltage is 12 V:
Itotal = V / Req = 12 / 66.6667 = 0.18 A
Total power:
P = V × I = 12 × 0.18 = 2.16 W
Common mistakes to avoid
- Adding resistors directly for parallel circuits. Direct addition only applies to series circuits.
- Mixing units (ohms, kilo-ohms, mega-ohms) without converting first.
- Ignoring tolerance. Real resistors often vary by ±1%, ±5%, or more.
- Confusing branch and total current. Branch current is V/R for that branch, while total current is the sum of all branch currents.
Practical applications
This type of calculation is useful in many electronics and electrical tasks:
- Designing LED resistor networks
- Estimating effective load on power supplies
- Sensor interface circuits
- Audio crossover and filtering experiments
- Quick troubleshooting on breadboards or prototype boards
Frequently asked questions
Can equivalent resistance be higher than the smallest resistor in parallel?
No. In parallel, equivalent resistance is always less than the smallest branch resistance.
Can I enter only one resistor?
Yes. The equivalent resistance is simply that resistor value.
What if I leave voltage blank?
The calculator still computes equivalent resistance, but skips current and power calculations.
Does this support mixed series-parallel circuits?
This page is focused on a pure parallel block. For mixed networks, reduce each section step-by-step (series first where obvious, then parallel), or use a full network solver.