Resistor colour code calculator
Resistor value from its four colour bands, with the tolerance range.
Fill in the fields and the result will appear here automatically.
Decode the supported four-band marking: two significant digits, a decimal multiplier and tolerance. Available digits are 0–9, multipliers 10⁻²…10⁷ and tolerances 1,2,5,10%. Results show nominal resistance and arithmetic tolerance bounds under component specification conditions, not measured resistance or an automatic fault diagnosis.
How it works
Formula and logic
R=(10 b₁+b₂)·10^m; Rmin=R(1−t/100), Rmax=R(1+t/100), span=2 Rt/100. A gold multiplier is 0.1; silver is 0.01. Colour roles differ: gold tolerance means 5% here. Unknown codes and fractional digit selections are rejected.
Example
Yellow 4, violet 7, red ×100 and gold±5% give 4700 Ω, bounds 4465…4935 Ω and span 470 Ω. With the same first digits a gold multiplier gives 4.7 Ω and silver gives 0.47 Ω. Gold does not make every resistor smaller than 1 Ω.
Fields and units
- First band — first digit — list option
- Second band — second digit — list option
- Third band — multiplier — list option
- Fourth band — tolerance — list option
How to use
- — Place the separated tolerance band on the right; it need not be gold or silver.
- — Choose exactly four supported bands in reading order.
- — Check component documentation if orientation or band count is ambiguous.
- — Resistance measurement needs an unpowered component and removal of parallel-path influence; the bounds do not classify every in-circuit reading.
Method and limitations
- Calculation method
- Formula and logic
- Data or methodology source
- Vishay: colour-code digits, multipliers and tolerances
- Limitation
- Arithmetic decoding of selected four bands; tolerance depends on specification conditions and does not prove component condition.
FAQ
Which end do I read from?
The separated tolerance band usually goes on the right. Brown±1% and red±2% are also available, so gold or silver is not a required end marker.
Why does the measured resistance differ from the nominal?
The marking specifies tolerance under stated conditions. For 4.7 kΩ±5%, bounds are 4.465…4.935 kΩ. Temperature, meter accuracy and parallel paths affect measurements; any reading inside those bounds does not prove component condition.
What do silver and gold multiplier bands mean?
Gold multiplies the significant digits by 0.1, silver by 0.01. Thus 47 becomes 4.7 Ω or 0.47 Ω. The first two digits still matter, and colour alone does not determine the application.
What about five bands?
Five bands normally provide three significant digits before multiplier and tolerance. More digits do not by themselves guarantee lower tolerance. This page accepts only the selected four-band model.