Resistor Calculator

The Formula

ResistorAn electrical component that opposes current flow. Resistance is measured in ohms (Ω) and follows Ohm's Law. color codes use bands to encode the resistance value, multiplier, and tolerance. The first bands are significant figures, followed by a multiplier band and a tolerance band.

Variable Definitions

How to Use This Calculator

1. 1

   Select Forward mode to decode resistor color bands into a resistance value.

2. 2

   Select Reverse mode to find the color code for a desired resistance value.

3. 3

   Choose the number of bands (4, 5, or 6) matching your resistor.

4. 4

   For forward mode, pick the color of each band from the dropdown menus.

5. 5

   For reverse mode, enter the desired resistance value.

4-band resistor color code: first two bands are digits, third is multiplier, fourth is tolerance

Understanding the Concept

ResistorAn electrical component that opposes current flow. Resistance is measured in ohms (Ω) and follows Ohm's Law. color codes are a standardized system for marking resistance values on through-hole resistors. The first bands represent significant digits, the next band is the decimal multiplier, and the last band(s) indicate tolerance and temperature coefficient. For 4-band resistors, the first two bands are digits, the third is the multiplier, and the fourth is the tolerance. Practical example: a resistor with Brown-Black-Red-Gold bands. Brown = 1, Black = 0, so the significant digits are 10. Red multiplier = 100, so the resistance is 10 × 100 = 1,000 ohms (1 kΩ). Gold tolerance = ±5%, so the actual value is between 950 Ω and 1,050 Ω. Another example: Yellow-Violet-Orange-Silver = 47 × 1,000 = 47 kΩ at ±10% (range: 42.3 kΩ to 51.7 kΩ). Edge cases: for surface-mount resistors (SMD), color codes are not used — instead, a three- or four-digit numbering system is used. A marking of "472" means 47 × 10² = 4,700 Ω. The letter "R" indicates a decimal point, so "4R7" = 4.7 Ω. For zero-ohm jumpers (used as wire bridges on PCBs), a single black band or a "0" marking is used. When reading vintage resistors, the body-end-dot system (used before the band system was standardized in the 1950s) may be encountered: the body color is the first digit, the end color is the second digit, and the dot color is the multiplier.

Frequently Asked Questions

Sources & References