Question 1

How do I calculate resistors in series?

Accepted Answer

Resistors in series simply add: Rs = R1 + R2 + R3 + ... For example, 100 ohms in series with 220 ohms gives 320 ohms. The total is always larger than the largest single resistor.

Question 2

How do I calculate resistors in parallel?

Accepted Answer

For parallel resistors, add the reciprocals and invert: 1/Rp = 1/R1 + 1/R2 + ... For exactly two resistors this simplifies to Rp = (R1 x R2) / (R1 + R2). For example, two 100 ohm resistors in parallel give 50 ohms.

Question 3

Is parallel resistance always smaller than the smallest resistor?

Accepted Answer

Yes. The equivalent parallel resistance is always lower than the smallest resistor in the group, because each extra path gives the current another way to flow. Two equal resistors in parallel give exactly half their value.

Question 4

How can I make a resistor value I cannot buy?

Accepted Answer

Combine two standard E12 or E24 resistors. Two in series add up, and two in parallel give a lower value. This calculator's target finder searches the preferred series and shows the closest series and parallel pair to any value you enter, such as 3.3 kohm or 1.5 kohm.

Question 5

Does this calculator work for any number of resistors?

Accepted Answer

Yes. Add as many resistor rows as you need; each can use ohms, kiloohms, or megaohms. Empty or zero rows are ignored, and both the series total and the parallel equivalent update instantly in your browser.

Resistor Series& Parallel Calculator

Resistor Series
& Parallel Calculator