Resistor Color Code
Decode resistor color bands and reverse lookup standard color codes
About this calculator
The Resistor Color Code Calculator decodes 4-band and 5-band resistor color codes into a resistance value with its tolerance, and also works in reverse — enter a resistance and it finds the nearest standard band colors. It reports the nominal value in ohms plus the minimum and maximum resistance implied by the tolerance band, and flags impossible codes such as a black first band.
How to use the Resistor Color Code calculator
- Enter the quantities you know, using the units shown on each field.
- Read the computed results — they update instantly as you type.
- Use the visual explanation to see how the quantities relate.
- Copy the page URL to share the exact calculation.
Common examples
- Brown-black-red, gold → 1000 Ω ±5% (950 Ω to 1050 Ω)
- Yellow-violet-orange, gold → 47000 Ω ±5% (44650 Ω to 49350 Ω)
- 5-band brown-black-black-brown, brown → 1000 Ω ±1% (990 Ω to 1010 Ω)
- Reverse lookup 4700 Ω, 4 bands → yellow-violet-red, gold
- Reverse lookup 220 Ω → red-red-brown, gold (209 Ω to 231 Ω at ±5%)
Frequently asked questions
How does the Resistor Color Code calculator work?
Enter the known quantities and the calculator applies the governing physical law or scientific formula to find the unknowns, stating the equation it used and the units of every result. Computations run at high precision.
When would I use the Resistor Color Code calculator?
It suits physics and chemistry homework, lab work, engineering estimates, and any time you want to explore how changing one quantity affects the others in a well-defined scientific relationship.
How accurate are the results?
The formula itself is evaluated at 30 significant digits of precision. Keep in mind that idealized models — such as neglecting friction, air resistance or measurement error — bound the real-world accuracy more than the arithmetic does.
Can I share a specific calculation with someone else?
Yes. Every value you enter updates the URL, so copying the address bar and sharing the link reopens the exact same calculation for whoever clicks it.