Series & Parallel Resistor Calculator

Calculates total resistance for resistors in series (add values) or parallel (add reciprocals). Also shows current and power distribution across each resistor. Worked example: 1 kohm and 2 kohm in parallel give R = (1000x2000)/(1000+2000) = 666.7 ohm; the same pair in series gives 3 kohm. At 9 V the parallel pair draws 13.5 mA. For three or more parallel resistors keep adding conductances: 1k, 2k, and 4k in parallel settle at 571.4 ohm because 1/Rt = 0.001 + 0.0005 + 0.00025 - always below the smallest branch.

1. 1

   Step 1

   Select connection type (series or parallel)

2. 2

   Step 2

   Enter the supply voltage

3. 3

   Step 3

   Add resistor values one by one

4. 4

   Step 4

   View total resistance and individual results

• 1

  Series: same current, voltage divides proportionally

• 2

  Parallel: same voltage, current divides inversely

• 3

  Total parallel resistance is always less than smallest resistor

• 4

  Use 1% resistors for precision voltage dividers

• Using series formula for parallel circuits

• Forgetting that parallel resistance is less than any single resistor

• Not checking individual resistor power ratings

• Mixing series and parallel formulas in complex networks