Resistor Calculator
Add resistors in series or parallel, read a resistor’s colour bands, or find the colour bands for a value. Every answer comes with simple steps, one at a time.
Type values separated by commas or spaces. You can write 470, 4.7k, 2.2M, or the electronics style 4k7 and 2M2.
Series and parallel formulas
| Connection | Total resistance | Note |
|---|---|---|
| Series | R = R1 + R2 + … | Same current in every resistor |
| Parallel | 1/R = 1/R1 + 1/R2 + … | Same voltage across every resistor |
| Two in parallel | R = R1R2 / (R1 + R2) | Always smaller than the smaller one |
Resistor colour code chart
| Colour | Digit | Multiplier | Tolerance | Temp. (ppm/°C) |
|---|
How to read the bands
For 4 bands: the first two are digits, the third is the multiplier, the fourth is the tolerance. For 5 bands the first three are digits. A sixth band gives the temperature coefficient. Example: brown, black, red, gold = 1, 0, ×100, ±5% = 1 kΩ ±5%.
FAQ
How do I calculate resistors in series?
Add them: R = R1 + R2 + R3. For example 100 ohm, 220 ohm and 330 ohm in series give 650 ohm.
How do I calculate resistors in parallel?
Add the reciprocals and flip the result: 1/R = 1/R1 + 1/R2 + ... For two resistors, R = R1 x R2 / (R1 + R2). The total is always smaller than the smallest resistor.
How do I read a 4-band resistor?
The first two bands are digits, the third is the multiplier and the fourth is the tolerance. Brown, black, red, gold is 10 x 100 = 1000 ohm with 5 percent tolerance.
What does a 5-band resistor mean?
The first three bands are digits, the fourth is the multiplier and the fifth is the tolerance. It shows three digits, so it is more precise than a 4-band resistor.
What are the resistor colour code values?
Black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, grey 8, white 9. Gold and silver as multipliers are x0.1 and x0.01, and as tolerance +/-5 and +/-10 percent.
What does 4k7 mean on a resistor?
It is the electronics way of writing 4.7 kilo-ohm, with the letter k in the place of the decimal point. In the same way 2M2 is 2.2 mega-ohm and 4R7 is 4.7 ohm.