Free Resistor Calculator Online
Use this free resistor calculator to decode color bands into resistance values. Select 4-band or 5-band mode, pick your colors, and instantly see the resistance in ohms along with tolerance. The resistor calculator also shows a visual band diagram so you can confirm your reading.
Resistance Value
Select color bands to decode
How the Resistor Calculator Works
Every through-hole resistor is marked with colored bands that encode its value. The resistor calculator reads these bands using the standard EIA color code: each color maps to a digit (0-9), a multiplier (1 to 10M), or a tolerance value (1-20%).
For a 4-band resistor with red-violet-orange-gold bands, the resistor calculator decodes this as: 2 (red) 7 (violet) x 1,000 (orange) = 27,000 ohms (27K) with 5% (gold) tolerance. That means the actual value falls between 25,650 and 28,350 ohms.
Five-band precision resistors add an extra digit. A brown-red- black-brown-brown resistor reads 120 x 10 = 1,200 ohms with 1% tolerance. The resistor calculator handles both formats and shows results in a readable format with proper unit prefixes.
Resistor Color Code Reference
Gold and silver bands are used for tolerance (5% and 10%) and fractional multipliers (0.1 and 0.01). See the full table in the resistor calculator above.
Common Resistor Values
E12 Series
The E12 series has 12 values per decade: 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, and 82. These are the most commonly stocked 10% tolerance resistors and cover most hobby and prototyping needs.
E24 Series
The E24 series adds intermediate values for 5% tolerance resistors. It includes all E12 values plus 11, 13, 16, 20, 24, 30, 36, 43, 51, 62, 75, and 91. These give tighter value spacing for precision circuits.
Power Ratings
Standard through-hole resistors are rated at 1/4W or 1/2W. If your circuit pushes more power through a resistor, you need a higher wattage part. Use the Ohms Law calculator alongside the resistor calculator to check power dissipation.
Frequently Asked Questions
Disclaimer: This resistor calculator provides standard color code values. Actual resistance may vary within the stated tolerance. Always measure with a multimeter for precision applications.