Formulas and sources
Each formula this calculator uses, where it comes from, and what it leaves out. "How it works" shows the same formula with your own numbers.
Reading the color bands
Decode and Batch modes
- R
- resistance, in ohms
The first line is a 4-band part, the second a 5- or 6-band part. Each color stands for a digit, a multiplier, a tolerance or, on a sixth band, a temperature coefficient in ppm/K. Read from the end opposite the tolerance band.
Source: Uses the color code of IEC 60062:2016, Table 1; every color this tool offers matches it [1].
Tolerance range
Decode, Encode and SMD modes
- R
- resistance, in ohms
- ±
- the tolerance range either side
- t
- tolerance, in percent, from the tolerance band
Source: Standard arithmetic; the tolerance colors are those of IEC 60062:2016, Table 1 [1].
Nearest standard value
Encode mode
The target is matched to the nearest E24 or E96 value by ratio, over multipliers from ×0.01 to ×10⁹. E24 has 24 values a decade and E96 has 96. The Sourcing Hints in every mode use the same rule.
Source: Based on the E series of IEC 60063:2015 [2], which this page did not read. The E96 values equal round(100 × 10^(i/96)); the E24 list equals ROHM's published table. The nearest-by-ratio rule is CalcTrail's own; no publisher.
SMD markings
SMD and Batch modes
- R
- resistance, in ohms
Three digits, then four. In the letter code, R, K or M marks the decimal point: 4R7 is 4.7 Ω, 47K is 47 kΩ. Two digits and another letter are read as EIA-96: the digits pick an E96 value, the letter its multiplier.
Source: The digit and letter codes follow IEC 60062:2016, clause 4 and Tables 2 to 4 [1]. EIA-96 is widely used; no primary source found for its letters (IEC 60062 and the IEC catalogue searched). The ±5% or ±1% range an SMD result assumes is CalcTrail's own; no publisher.
Sources
- International Electrotechnical Commission (IEC). IEC 60062:2016, Marking codes for resistors and capacitors, clause 3, Table 1 (colour code); clause 4, Tables 2 to 4 (letter and digit codes). Edition 6.0, July 12, 2016.
- International Electrotechnical Commission (IEC). IEC 60063:2015, Preferred number series for resistors and capacitors. Edition 3.0, March 27, 2015.
What this calculator does not cover
- A printed SMD marking carries no tolerance. The range shown assumes ±5% for a three-character code and ±1% for four characters or EIA-96.
- It does not read three-band (±20%) parts, the pink (×0.001) multiplier, a trailing tolerance letter ("4K7F") or the L and G letters of the letter code, all in IEC 60062.
- It reads resistor codes only, not capacitor or inductor codes, and a zero-ohm part reads as 0 Ω.
- It offers only the E24 and E96 series, and it does not combine two parts into one value.
Sources checked on .