Resistor Calculator

About the Resistor Calculator

A resistor calculator decodes the colour band system on standard resistors to reveal their resistance value and tolerance, or generates the correct colour code for any target resistance value. Reading resistor colour codes is one of the fundamental practical skills in electronics — required every time you identify a component value from a physical resistor, specify resistors for a schematic, or verify that the parts bin contains the right values. Our calculator handles 4-band resistors (most common), 5-band resistors (1% tolerance, precision), and 6-band resistors (additional temperature coefficient band), plus the E12, E24, E48, and E96 preferred value series finder for identifying the closest available standard value to any target. It also includes a parallel and series resistance calculator for designing custom resistance values from standard parts.

How It Works

Standard resistor colour code (each colour = a digit or multiplier): Black=0, Brown=1, Red=2, Orange=3, Yellow=4, Green=5, Blue=6, Violet=7, Grey=8, White=9. 4-band: bands 1-2 = two significant digits, band 3 = multiplier (power of 10), band 4 = tolerance. Example: Brown-Red-Orange-Gold = 1, 2, ×1000, ±5% = 12,000Ω = 12 kΩ ±5%. Gold multiplier = ×0.1; Silver = ×0.01. Tolerance bands: Gold = ±5%, Silver = ±10%, Brown = ±1%, Red = ±2%. 5-band: three significant digits + multiplier + tolerance. Brown-Black-Black-Brown-Brown = 1,0,0, ×10, ±1% = 1,000Ω = 1 kΩ ±1%. Preferred value series: the E12 series (12 values per decade) provides 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82 and their decade multiples.

Tips & Best Practices

• ✓Memory aid: "BB ROY of Great Britain has a Very Good Wife" — Black(0) Brown(1) Red(2) Orange(3) Yellow(4) Green(5) Blue(6) Violet(7) Gray(8) White(9).
• ✓Gold and silver are always in the last (tolerance) position — they never appear as digit or multiplier bands. If you see gold or silver, orient the resistor so they are on the right.
• ✓Two equal resistors in parallel = half the value of either one. Three equal resistors in parallel = one-third. Four in parallel = one-quarter. This scaling applies for any number n of equal resistors: parallel result = R/n.
• ✓Preferred E-series values: resistors are only manufactured in E-series values (E12, E24, E96, E192 for progressively finer tolerances). The E12 series provides 12 values per decade; E96 provides 96 values for ±1% precision work.
• ✓Temperature coefficient (TC): the 6th band on precision resistors indicates TC in ppm/°C. Brown = 100 ppm/°C; Red = 50; Orange = 15; Yellow = 25; Green = 20; Blue = 10; Violet = 5. Precision audio and instrumentation applications specify TC.
• ✓Reading direction: read from the end with bands closest to the edge. On a 4-band resistor, the first significant digit band is typically closest to one end. When uncertain, calculate both directions and select the one that gives an E-series standard value.
• ✓Parallel resistance for non-equal values: use 1/R_total = 1/R₁ + 1/R₂ + ... For two resistors: R_total = (R₁ × R₂) / (R₁ + R₂). Example: 4.7 kΩ parallel with 10 kΩ = (4,700 × 10,000)/(4,700+10,000) = 47,000,000/14,700 = 3.197 kΩ.
• ✓SMD resistors (surface-mount): use a 3- or 4-digit code instead of colour bands. "472" = 47 × 10² = 4,700Ω. "4702" = 470 × 10² = 47,000Ω = 47 kΩ. The EIA-96 code uses a two-character code referencing the E96 series.

Who Uses This Calculator

Electronics beginners building first circuits from schematics. Students in introductory electronics courses learning colour code identification. Hobbyists sorting and identifying resistors from mixed component bins. Repair technicians identifying damaged or faded components. Teachers creating colour code exercises with known answers. PCB designers selecting standard values for prototype circuits. Makers designing LED, sensor, and motor control circuits with appropriate current-limiting resistors.