Resistors in Series and Parallel Calculator
Type your resistor values, one per line or separated by commas. You get the series total and the parallel total together.
Write values as 4.7k, 100, 2M2, 4k7 or 0.5. The letter k means thousand and M means million. An optional unit such as ohm is ignored.
Worked examples
Two equal parts
100 and 100
200 ohms in series and 50 ohms in parallel
Equal resistors in parallel halve the value.
Three values
100, 200 and 300
600 ohms in series, 54.5 ohms in parallel
1 / (1/100 + 1/200 + 1/300).
About Resistors in Series and Parallel Calculator
When resistors are joined end to end, the same current flows through all of them and their values add up. When they are joined across the same two points, the current splits and the combined resistance is smaller than the smallest one. This calculator takes a list of values and gives the total for both arrangements at the same time, so you can compare them straight away.
Values can be typed the way they are written on circuit diagrams: 4.7k, 4k7, 2M2, 100 or 0.5. You can use as many resistors as you like, one per line or separated by commas. Add a supply voltage to see the current each arrangement would draw, and a table shows the share of the series total taken by each part, which helps when you are building an unusual value from standard resistors.
How to use Resistors in Series and Parallel Calculator
- Type or paste your resistor values, one per line or separated by commas.
- Use the usual shorthand: k for thousand, M for million, or 4k7 for 4,700.
- Optionally enter a supply voltage to see the current in each arrangement.
- Read the series and parallel totals and the table of shares.
Common uses
- Making a non-standard resistance from two or three standard parts
- Checking the total of a chain of resistors on a schematic
- Finding the combined resistance of heating elements
- Homework on series and parallel circuits
Frequently asked questions
What is the formula for resistors in parallel?
The reciprocal of the total is the sum of the reciprocals: 1 / R = 1 / R1 + 1 / R2 + 1 / R3 and so on. For two resistors this simplifies to the product divided by the sum.
Why is the parallel total smaller than any single resistor?
Each extra path gives the current another route, so it is easier for current to flow. Two equal resistors in parallel give exactly half the value.
What does 4k7 mean?
It is a way of writing 4.7 kilohms, or 4,700 ohms, without a decimal point that could get lost in print. The letter stands where the point would be.
Do power ratings add up too?
Only if the resistors share the load equally, which needs equal values. With unequal values, the smaller resistor takes more current in parallel and more voltage in series, so check each one.