Resistor Color Code Calculator:
Decode bands, LEDs & Ohm's Law
Decode 4-band, 5-band, and 6-band resistor color codes instantly. Calculate LED current-limiting resistors with wattage warnings. Solve Ohm's Law for any variable. Includes SMD decoder, colorblind-friendly mode, and GPIO presets for Arduino and Raspberry Pi.
Resistor Bands
Reverse Lookup: Value to Colors
SMD Resistor Code Decoder
Results
Select colors or enter values to see results.
How it works
Choose your mode
Switch between the resistor color code decoder, Ohm's Law calculator, and LED resistor calculator. Each mode is optimized for a specific electronics task.
Enter your values
Click color bands, type SMD codes, or enter voltage and current values. Use GPIO presets for Arduino and Raspberry Pi to skip manual setup.
Get instant results
See resistance values, tolerance ranges, standard E-series recommendations, power dissipation, and wattage warnings. Everything updates instantly as you type.
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Frequently asked questions
What is the Best Answer Hub Resistor Color Code Calculator?
The Best Answer Hub Resistor Color Code Calculator is a free, browser-based electronics tool that decodes 4-band, 5-band, and 6-band resistor color codes into resistance values, tolerances, and temperature coefficients. It also includes an Ohm's Law solver and an LED resistor calculator with wattage warnings and standard E-series value recommendations. Every calculation runs instantly in your browser with no signup required.
Which way do you read resistor color codes when both ends look the same?
Start from the end closest to a gold or silver tolerance band, which is always the last band. If there is no obvious tolerance band, look for a wider gap between the last band and the rest. The isolated band is the tolerance. On 5-band resistors, the tolerance band is often brown (1%) or red (2%) and sits slightly apart from the value bands. The Best Answer Hub Resistor Color Code Calculator shows a visual resistor diagram that highlights the reading direction automatically.
What is the difference between a 4-band and a 5-band resistor?
A 4-band resistor uses two significant digits, a multiplier, and a tolerance band. A 5-band resistor uses three significant digits, a multiplier, and a tolerance band, giving ten times more precision. For example, a 4-band resistor showing brown-black-red-gold is 1,000 ohms with 5% tolerance. A 5-band resistor showing brown-black-black-brown-brown is 1,000 ohms with 1% tolerance. The extra digit matters in precision circuits like audio amplifiers and sensor bridges.
What size resistor do I need for a 5mm red LED on an Arduino 5V pin?
Use the formula R = (V_supply minus V_LED) divided by I. For a standard red LED with a 2.0V forward voltage and 20mA current on a 5V Arduino pin, the calculation is (5.0 minus 2.0) divided by 0.020 = 150 ohms. A 220 ohm resistor is the common safe choice because it limits current to about 14mA, which is bright enough and leaves headroom below the Arduino pin's 40mA absolute maximum. The Best Answer Hub LED Resistor Calculator includes Arduino 5V and 3.3V presets.
I know V=IR, but how do I actually use Ohm's Law to find the right resistor?
Rearrange the formula to R = V divided by I, where V is the voltage across the resistor and I is the current you want to flow through it. In an LED circuit, V is the supply voltage minus the LED forward voltage drop. For a 9V battery driving a blue LED with a 3.2V forward voltage, the voltage across the resistor is 9.0 minus 3.2 = 5.8V. At 20mA, R = 5.8 divided by 0.020 = 290 ohms. The nearest standard E12 value is 270 ohms or 330 ohms.
Why do Arduino tutorials always use 220 ohm resistors with LEDs?
The 220 ohm value is a safe, round-number compromise that works with almost any common LED on a 5V Arduino pin. For a red LED with a 2.0V drop, 220 ohms limits current to about 14mA. For a blue LED with a 3.2V drop, it limits current to about 8mA. Both values are well below the 20mA typical rating and far below the Arduino pin's 40mA maximum. The Best Answer Hub LED Resistor Calculator shows the exact current for any LED color and explains why 220 ohms is the universal starting point.
What happens if I don't use a resistor with my LED?
The LED will draw excessive current, overheat, and burn out within seconds, often with a visible pop or a darkened lens. Without a current-limiting resistor, the LED acts like a near-short circuit. A 5V supply directly across a red LED can push 100mA or more through it, which is five times its rated current. The Best Answer Hub LED Resistor Calculator always warns when no resistor is selected and shows the safe current range for any LED type.
Why does my multimeter read 215 ohms on a resistor that should be 220 ohms?
That reading is completely normal. A 220 ohm resistor with a 5% tolerance is guaranteed to be between 209 and 231 ohms. A 215 ohm reading falls comfortably inside that range. A 1% tolerance 220 ohm resistor should read between 217.8 and 222.2 ohms, so 215 would be slightly out of spec. The Best Answer Hub Resistor Color Code Calculator displays the tolerance range alongside the nominal value so you can verify any multimeter reading instantly.
How do I know what wattage resistor to use?
Calculate the power dissipated using P = V times I or P = I squared times R. For a 220 ohm resistor driving a red LED at 14mA on 5V, the power is 0.014 times 0.014 times 220 = 0.043 watts. A standard 1/4 watt (0.25W) resistor has plenty of headroom. For a 12V supply with a 470 ohm resistor at 25mA, the power is 0.025 times 0.025 times 470 = 0.294 watts, which exceeds a 1/4 watt rating and requires a 1/2 watt resistor. The Best Answer Hub LED Resistor Calculator computes wattage automatically and warns if your selected resistor is undersized.
How do you read SMD resistor codes like 103 or 4R7?
A 3-digit SMD code uses the first two digits as significant figures and the third digit as the multiplier in powers of ten. Code 103 means 10 times 10 to the power of 3 = 10,000 ohms = 10 kOhm. Code 4R7 means 4.7 ohms, where the R acts as a decimal point. A 4-digit code like 1002 means 100 times 10 to the power of 2 = 10,000 ohms = 10 kOhm. Code 0R00 or 000 is a zero ohm jumper. The Best Answer Hub Resistor Color Code Calculator includes an SMD mode that decodes 3-digit, 4-digit, and EIA-96 codes instantly.
How can I read resistor colors if I'm colorblind?
Use a calculator that labels every color with its name rather than relying on color vision alone. The Best Answer Hub Resistor Color Code Calculator includes a text-only mode where you select band colors from a labeled dropdown menu. Each option shows the color name and its numeric value, so red-brown-orange-gold becomes a sequence of text labels rather than a color-matching exercise. You can also use a multimeter to verify the value after selecting the bands.
I calculated 350 ohms for my LED but my kit only has 330 and 470, so which one is safer?
Always choose the next higher standard value, which is 470 ohms in this case. A higher resistor value reduces current, which makes the LED dimmer but never damages it. A lower value like 330 ohms increases current beyond your calculated safe level, which can overstress the LED or exceed your GPIO pin's current limit. The Best Answer Hub LED Resistor Calculator automatically rounds up to the nearest E12 or E24 standard value and shows the actual current at that resistance.
Do I need to recalculate the resistor if I swap a red LED for a blue one?
Yes. Red LEDs typically have a 1.8V to 2.2V forward voltage drop, while blue and white LEDs drop 3.0V to 3.4V. On a 5V supply, the voltage across the resistor changes from about 3.0V to about 1.8V. Using the same 220 ohm resistor, a red LED runs at 14mA but a blue LED runs at only 8mA, which may be too dim. For bright blue or white LEDs, you often need a lower resistor value like 150 ohms. The Best Answer Hub LED Resistor Calculator has presets for common LED colors that automatically adjust the forward voltage.
How do I read a 6-band resistor with temperature coefficient?
A 6-band resistor uses three significant digits, a multiplier, a tolerance band, and a sixth band that indicates the temperature coefficient in parts per million per degree Celsius. Brown on the sixth band means 100 ppm per degree Celsius, red means 50 ppm, orange means 15 ppm, and yellow means 25 ppm. A 100 ppm resistor changes by 0.01% for every degree of temperature change. The Best Answer Hub Resistor Color Code Calculator decodes all six bands and explains what the temperature coefficient means for circuit stability.
Do I need a resistor if I'm powering an LED from a 3.3V Raspberry Pi GPIO pin?
Yes, always. Even at 3.3V, a red LED with a 2.0V forward voltage will try to draw excessive current without a resistor. The calculation is (3.3 minus 2.0) divided by R. Without a resistor, R is effectively zero and current is limited only by the GPIO pin's internal resistance, which can still exceed the LED's rating and the Pi's 16mA per-pin maximum. A 68 ohm resistor limits current to about 19mA, which is safe for the LED but close to the Pi's limit. A 100 ohm resistor at 13mA is the safer choice. The Best Answer Hub LED Resistor Calculator includes a Raspberry Pi 3.3V preset with conservative current limits.
What people use it for
Common use cases from electronics students, Arduino hobbyists, and repair technicians.
Pick the right LED resistor every time
Arduino 5V + GPIO presets
Select the Arduino 5V preset, choose your LED color, and get the exact resistor value with wattage check. Never guess between 220 ohms and 330 ohms again. See the actual current and brightness for each standard value.
Decode faded or damaged resistor bands
Text-only mode + tolerance range
When color bands are faded or burned, use the text-only colorblind-friendly mode to select bands by name. Verify the decoded value against the tolerance range, then confirm with a multimeter reading.
Learn Ohm's Law with real circuit numbers
V=IR + power calculation
Enter any two values in the Ohm's Law calculator to solve for the third. See power dissipation in watts instantly. Understand why a 1/4 watt resistor is fine for a 5V LED circuit but fails on a 12V supply.
Find standard resistor values from calculations
E12 / E24 auto-round-up
When your calculation gives 347 ohms but your kit only has 330 and 470, the calculator automatically rounds up to the safe standard value and shows the exact current at that resistance. No more fried LEDs from guessing low.
Built & maintained by Shahbaz Ali Malik Last updated: