Calculator Inputs
Use the responsive grid below. Large screens show three columns, smaller screens show two, and mobile uses one column.
Example Data Table
These examples show how the calculator behaves with common circuit arrangements.
| Example | Mode | Resistor inputs | Voltage | Equivalent resistance | Total current |
|---|---|---|---|---|---|
| 1 | Series | 10 Ω, 20 Ω, 30 Ω | 12 V | 60 Ω | 0.2000 A |
| 2 | Parallel | 10 Ω, 20 Ω, 30 Ω | 12 V | 5.4545 Ω | 2.2000 A |
| 3 | Series-Parallel Branches | B1: 10 Ω + 20 Ω, B2: 15 Ω + 15 Ω, B3: 60 Ω | 12 V | 12 Ω | 1.0000 A |
| 4 | Series | 2.2 kΩ, 3.3 kΩ, 4.7 kΩ | 9 V | 10.2 kΩ | 0.000882 A |
Formula Used
The calculator applies standard resistance relationships and optional electrical follow-up values.
1) Series total resistance
RT = R1 + R2 + R3 + ... + Rn. Every resistor simply adds to the total because the same current flows through each component.
2) Parallel total resistance
1 / RT = 1 / R1 + 1 / R2 + 1 / R3 + ... + 1 / Rn. The final equivalent is the reciprocal of the reciprocal sum.
3) Series-parallel branches
First, each branch is solved as a series string: Rbranch = ΣR. Then all finished branch totals are combined in parallel with 1 / RT = Σ(1 / Rbranch).
4) Optional current and power
When source voltage is provided, the calculator uses I = V / RT and P = V × I = V² / RT. It also estimates branch currents, resistor voltage drops, and resistor power values.
5) Tolerance range estimate
If you enter a tolerance percent, the calculator scales every resistor by (1 − t) and (1 + t), then recalculates the network to estimate minimum and maximum equivalent resistance.
How to Use This Calculator
Follow these steps for a clean and consistent workflow.
Frequently Asked Questions
These short answers cover common design and usage questions.
1) What does total resistance mean?
Total resistance is the single equivalent value that can replace an entire resistor network without changing the source behavior seen by the rest of the circuit.
2) When should I use series mode?
Use series mode when current flows through one continuous path and every resistor carries the same current from the source to the load.
3) When should I use parallel mode?
Use parallel mode when all resistor ends connect across the same two nodes, meaning each branch sees the same voltage.
4) How does series-parallel mode work here?
You group components with the same branch ID. Each group is added in series first. Then the finished branch totals are combined in parallel.
5) Why is the total resistance lower in parallel circuits?
Parallel branches create additional current paths. More paths reduce the network opposition to current, so the equivalent resistance becomes lower than the smallest branch.
6) Why add source voltage?
Voltage is optional, but it unlocks useful outputs such as total current, component voltage drops, branch currents, and power dissipation estimates.
7) What does the tolerance range tell me?
It estimates how the equivalent resistance may shift when all active resistors vary by the same tolerance percentage above or below their nominal values.
8) Can I mix units inside one calculation?
This version expects one input unit per calculation. Convert values first if needed, or rerun the calculator after switching to the correct common unit.