Series Resistance Calculator
Enter any number of resistors connected end to end to get the total series resistance, with each one's share of the voltage.
How it works
Resistors in series carry the same current, and the voltages across them add up to the supply. That makes the total simply the sum of the individual values — no reciprocals involved.
The consequence worth remembering: the total is always larger than the largest single resistor. If your answer is smaller than one of the parts, the circuit is parallel, not series.
Because the same current flows through all of them, each resistor drops voltage in proportion to its own value. That is the entire basis of the voltage divider.
The formula
Total
R_total = R1 + R2 + R3 + …
Voltage across one resistor
V_n = V_supply × R_n ÷ R_total
Current (same everywhere)
I = V_supply ÷ R_total
Worked examples
| Scenario | Working | Result |
|---|---|---|
| 100 Ω + 220 Ω + 330 Ω | Straight sum | 650 Ω |
| Two 1 kΩ resistors in series | 1000 + 1000 | 2 kΩ |
| 1 kΩ + 2 kΩ across 9 V | 9 × 2000 ÷ 3000 | 6 V across the 2 kΩ |
When you'd use it
- Making up a value you do not have from ones you do
- Checking the total load a supply will see
- Working out the voltage at a point between two resistors
- Raising resistance to limit current in a test circuit
Common questions
Does the order of the resistors matter?
No. The total is the same whatever order they sit in, and so is the voltage across each one. Physical order only matters for layout and heat, not for the maths.
Can I combine tolerances the same way?
Not by simply adding the percentages. In the worst case the absolute errors add, so three ±5% resistors give a total that is still ±5% of the sum. Statistically the spread is usually tighter than that, but design for the worst case.
What about the power rating of the chain?
Each resistor dissipates I² × its own resistance, so the largest value in a series chain gets the hottest. Check that one against its rating rather than assuming the load is shared evenly.
Is anything I enter sent to a server?
No. Every calculation runs in your browser, so component values, circuit figures and measurements are never uploaded, logged or stored. There is no account and no record of what you typed.