Combine resistors to hit a target value

The job

Standard resistor kits skip most values. When a schematic calls for 3.4 kΩ and the drawer has 1k, 2.2k, 4.7k, the fix is usually two resistors: in series they add, in parallel the combined value dips below both. Enter what you have and the target; the pair finder says exactly what second resistor hits it, plus the closest E24 standard value.

Combining resistors

For a straight equivalent, enter your values and pick series or parallel. For the pair finder, enter the resistor you already have and the target resistance — the tool solves for the second one.

• Series adds: 1k + 2.4k = 3.4k.
• Parallel uses the reciprocal sum: 4.7k ∥ 12k ≈ 3.38k.
• The target must sit below your existing resistor for a parallel pair to reach it — parallel always lowers the total.

Worked example

Target 3.4k with a 4.7k on hand: the exact second resistor is ≈12.33kΩ. Nearest E24 is 12k, giving 4.7∥12 ≈ 3.38k — about 0.6% off the target, well inside a 5% or even 1% tolerance budget.

Where it stops

1–12 resistors, 0.001 Ω to 1 GΩ per run. The pair finder assumes a two-resistor solution; complex ladders and 0.1% precision work still need a solver or trimmer. Tolerance in the real parts isn't modelled — a nominal hit can drift a few percent in the build.