π Series Resistor Calculator
Calculate total resistance of resistors in series: Rt = R1+R2+...
Result
How to Use This Calculator
This calculator finds the total resistance of resistors connected in series. Enter two or more values and it adds them into one equivalent resistance.
Enter the first resistor value in ohms in the R1 field.
Enter the second in R2, and click the add button for more resistors.
Click Calculate. The total appears in ohms.
Check that the total is larger than your biggest single resistor. In series it always is.
Resistors in Series
Series means one path: the current has no choice but to march through each resistor in sequence. Each resistor contributes its full opposition, so the totals add directly. Contrast this with parallel, where extra branches give current more paths and the total drops. The series rule is the simpler of the two, but it is also the one students mix up with parallel under exam pressure.
Because the current is identical everywhere in a series chain, the voltage divides in proportion to resistance: the biggest resistor drops the most voltage. That proportional splitting is the entire principle behind voltage dividers, which step voltages down all over electronics.
Worked Example
Where This Comes Up
Series resistance shows up in LED current limiting (one resistor sets the current for the whole string), voltage dividers for sensors, and fuse-and-load arrangements where the same current must pass through protection and device. Guitar volume pots and old dimmer switches are variable series resistors.
The giveaway error is a series total smaller than the parts: you used the parallel formula by accident. Also watch for the hidden series resistor in real circuits: wires, connectors, and meter leads all add small resistances that matter in low-resistance measurements.
Frequently Asked Questions
Why do series resistances simply add?
The same current flows through each resistor in turn, and each one drops some voltage. The total voltage drop is the sum of the parts, so the equivalent resistance is the sum: R = R1 + R2 + ...
What happens if one resistor in series fails?
An open failure breaks the whole chain and current stops everywhere, which is why one dead bulb used to kill old series-wired Christmas lights. A shorted resistor just removes itself from the total.
How do I split a voltage with two resistors?
Use a voltage divider: Vout = Vin x R2 / (R1 + R2), measured across R2. It is the standard trick for scaling sensor signals down to what a microcontroller pin can read.
Does the order of resistors matter?
No. Addition commutes, so R1 + R2 equals R2 + R1. The total is the same regardless of sequence.
Series or parallel: which divides voltage?
Series divides voltage among components; parallel gives every component the full voltage. Pick series when you want to share voltage, parallel when each part needs the whole supply.