Calculation methods
The formulas, worked examples, assumptions and limits behind every tool.
Resistor colors ↗
Resistance = significant digits × 10^multiplier. Four bands use two digits; five bands use three.
Example: Brown, black, red, gold means 10 × 100 = 1,000 Ω, ±5%.
The first significant digit must be nonzero. Tolerance is decoded from its own band and is not a measured component value.
Resistor network ↗
Series R = ΣR. Parallel R = 1 ÷ Σ(1/R). All list entries share the selected unit.
Example: Two 1 kΩ resistors give 2 kΩ in series or 500 Ω in parallel.
Supports 1–12 positive entries. Selecting another unit reinterprets the list; it does not change the typed numbers. Ideal resistors are assumed.
Voltage divider ↗
Vout = Vin × Reffective ÷ (Rtop + Reffective). With a load, Reffective = Rbottom || Rload.
Example: 5 V across two 10 kΩ resistors gives 2.5 V unloaded; a 10 kΩ load changes it to about 1.667 V.
This is an ideal DC resistive model. It excludes source impedance, tolerance and dynamic loading. Inputs use volts and kΩ, with a 0–60 V model range.
RC time constant ↗
τ = RC. Charging V = Vin(1 − e^(−t/τ)); discharging V = Vin e^(−t/τ).
Example: 10 kΩ and 100 µF give τ = 1 s. After 1 s, a 5 V charge reaches about 3.161 V.
The charging model starts at 0 V, discharging at the entered initial voltage. Ideal components and a constant source are assumed.
Units and numerical limits
Conversions use 1 inch = 2.54 cm, 1 mile = 1.609344 km, and 1 avoirdupois ounce = 28.349523125 g. Empty, non-finite, out-of-range and unsupported values are rejected. Displayed values are rounded; calculations retain precision. Input-specific limits are reported alongside the field when exceeded.
RC time constant · DigiKey ↗