How to use
- Select Series or Parallel, choose the resistor count and one unit for every resistor. Enter R1 through the selected count; later fields are ignored.
- Press Calculate to view equivalent resistance and a diagram containing every active resistor. Copy result includes the mode and resistor values. Editing the count, mode, unit or any value clears the previous result.
Formula and interpretation
For series connections, R_eq = R1 + R2 + … + Rn. For parallel connections, 1/R_eq = 1/R1 + 1/R2 + … + 1/Rn. With two nonzero resistors this simplifies to R_eq = R1 × R2 / (R1 + R2). The diagram shows electrical connections, not a physical board layout.
Worked example
For R1 = 100 Ω and R2 = 300 Ω, series resistance is 400 Ω. The same two resistors in parallel give 75 Ω. For three equal 1 kΩ resistors in parallel, the equivalent is about 333.33 Ω.
Limits and input errors
Enter finite values from 0 to 10¹² in the selected unit. A zero-ohm resistor contributes zero in series; in parallel it shorts the branches and makes the equivalent zero. Only the first selected number of fields is used. Mixed series-parallel networks, open circuits, tolerances and component power ratings are not calculated.
Positive numeric inputs below 10⁻¹⁰⁰ are rejected to avoid numerical underflow. Use a decimal point or comma without grouping; scientific notation such as 1e-6 is accepted.
Frequently asked questions
Why is parallel resistance smaller than the smallest resistor?
Each positive branch provides another path for current. The total conductance increases, so the equivalent resistance falls. A zero-ohm branch is treated as an ideal short.
Can I mix ohms and kilohms?
The selected unit applies to all active fields. Convert first: 1 kΩ = 1,000 Ω and 1 MΩ = 1,000 kΩ. For example, use 1 and 0.47 in kΩ for 1 kΩ and 470 Ω.