Free Resistor Color Code Calculator — Decode Any Resistor Instantly

Need to read the color bands on a resistor? Looking up an SMD code? Calculating the right resistor for an LED circuit? Our free Resistor Calculator handles it all — color code decoding, SMD lookup, Ohm's Law, LED resistor sizing, voltage dividers, series/parallel combinations, and standard value finding. All in one tool, right in your browser.

Works in both directions: pick color bands to find the value, or enter a value to see which colors to look for. Supports 4-band and 5-band through-hole resistors plus 3-digit, 4-digit, and EIA-96 SMD codes.

What This Calculator Does

The Resistor Calculator combines eight essential electronics tools into a single tabbed interface. Every tool you need when working with resistors is here — from identifying an unknown resistor to designing circuits that need specific resistance values. No software to install, no account needed.

How to Use Each Tool

🎨 Color Bands — Read a Through-Hole Resistor

This is the classic resistor color code chart — but interactive. A realistic resistor graphic shows the colored bands on a tan body with wire leads. Click any band directly on the resistor to open a color picker for that position. You can also click the color dots below the resistor to change bands.

Toggle between 4-band (two significant digits + multiplier + tolerance) and 5-band (three significant digits + multiplier + tolerance) using the buttons at the top. The calculator instantly shows the resistance value, tolerance percentage, and the minimum-to-maximum range based on that tolerance.

The standard color code sequence is Black (0), Brown (1), Red (2), Orange (3), Yellow (4), Green (5), Blue (6), Violet (7), Grey (8), White (9). Gold and Silver are used for the multiplier band (×0.1 and ×0.01) and tolerance band (±5% and ±10%).

🔢 Value → Bands — Find Colors for a Known Value

Working the other direction — type a resistance value and see which color bands it corresponds to. Enter values in any common format: 4.7k, 470, 1M, 4K7 (European notation where the letter replaces the decimal point), 2R2 (2.2 ohms), or 330ohm.

The tool shows both the 4-band and 5-band color codes, each with a visual resistor graphic displaying the correct colors on the body. It also shows the nearest E24 standard value if your exact value doesn't fall on a standard resistor.

📐 SMD Code — Decode Surface Mount Resistors

Surface mount resistors use printed numeric codes instead of color bands. Enter the code printed on the component and the calculator identifies the value, code type, and tolerance. Four code formats are supported:

3-digit codes like "472" — the first two digits are significant (47) and the third is the number of zeros to add (2 zeros), giving 4,700Ω or 4.7kΩ. These are typically ±5% tolerance.

4-digit codes like "4702" — the first three digits are significant (470) and the fourth is the multiplier exponent, giving 47,000Ω or 47kΩ. These are typically ±1% precision resistors.

EIA-96 codes like "01A" — two digits reference a lookup table (01 = 100) and the letter indicates the multiplier (A = ×1), giving 100Ω. Used on ±1% precision SMD resistors.

R-notation like "4R7" — the letter R acts as a decimal point, so 4R7 means 4.7Ω. Used for low-value resistors where the number of digits would be ambiguous.

Click any of the four example cards below the input field to load that example and see how it decodes.

⚡ Ohm's Law — Calculate Voltage, Current, and Resistance

Ohm's Law states that voltage equals current times resistance: V = I × R. Enter any two of the three values — voltage in volts, current in milliamps, or resistance in ohms — and the calculator solves for the missing value plus power dissipation.

A circuit schematic shows the basic relationship: a voltage source connected through a resistor, with current flowing through the loop. The four key formulas are displayed: V = I × R (voltage), I = V / R (current), R = V / I (resistance), and P = V × I (power).

The power result includes a minimum wattage rating recommendation. If your resistor will dissipate 0.18W, the calculator tells you to use at least a ¼W resistor. This prevents the common beginner mistake of using an undersized resistor that overheats and fails.

💡 LED Resistor Calculator — Size the Right Current Limiting Resistor

Every LED needs a current-limiting resistor to prevent it from burning out. Enter your supply voltage (typically 3.3V, 5V, or 12V), the LED forward voltage (Red ≈ 2.0V, Green ≈ 2.2V, Blue/White ≈ 3.2V), the desired LED current (standard 20mA, or 2mA for low-power indicators), and the number of LEDs in series.

The calculator uses the formula R = (Vs - Vf) / I to determine the exact resistor needed, then shows the nearest E24 standard value with its 4-band color code displayed on a visual resistor graphic. It also shows voltage drop across the resistor, power dissipation, and the minimum wattage rating required.

A circuit schematic shows the correct wiring: power supply → resistor → LED → ground. The resistor always goes in series with the LED, and it does not matter whether the resistor is placed before or after the LED in the circuit.

🔋 Voltage Divider — Calculate Output Voltage from Two Resistors

A voltage divider uses two resistors in series to reduce a voltage. The output voltage is taken from the junction between the two resistors. The formula is Vout = Vin × R2 / (R1 + R2), where R1 is the "top" resistor connected to Vin and R2 is the "bottom" resistor connected to ground.

The calculator works in two modes. Enter all three values (Vin, R1, R2) to calculate Vout. Or enter Vin plus your desired Vout plus one resistor value, and it calculates the missing resistor with the nearest E24 standard value.

An ASCII circuit schematic shows the topology clearly. The results include current flowing through the divider and power dissipated by each resistor — important for ensuring your resistors can handle the load without overheating.

🔗 Series and Parallel Resistor Combiner

When you don't have the exact resistor value you need, you can combine standard values. Enter two or more resistor values separated by commas (any format — 1000, 2.2k, 4K7 all work) and the calculator shows both results simultaneously.

Series connection (resistors end-to-end): the total resistance is the sum of all values. Two 1kΩ resistors in series give 2kΩ. The schematic shows resistors connected in a chain.

Parallel connection (resistors side-by-side): the total resistance is always less than the smallest individual resistor. Two 1kΩ resistors in parallel give 500Ω. The formula is 1/Rt = 1/R1 + 1/R2. The schematic shows resistors connected between the same two points.

🔍 Standard Value Finder — Find the Closest Real Resistor

Resistors are manufactured in standard value series. When your calculation calls for 3,847Ω, you need to know which actual resistor to buy. Enter your target value and the finder shows the closest match in four standard series:

E12 — 12 values per decade, ±10% tolerance. The most basic series with widely available values. E24 — 24 values per decade, ±5% tolerance. The most commonly used series for general electronics. E48 — 48 values per decade, ±2% tolerance. For precision circuits. E96 — 96 values per decade, ±1% tolerance. For high-precision applications.

Below the single-resistor matches, the finder also searches for the best two-resistor combination from E24 standard values — both in series and parallel configurations. This often gets you much closer to your target than any single standard resistor can. For example, if you need 7.35kΩ, the finder might show that 3.6kΩ + 3.9kΩ in series gives 7.5kΩ (2% off), or 15kΩ ∥ 15kΩ gives 7.5kΩ.

Additional Features

↺ Reset button clears all inputs across all tabs and returns to the Color Bands tab. Light/dark theme toggle switches between a light interface and a dark mode that's easier on the eyes in dim environments — the setting is saved between visits. All calculations update instantly as you type with no need to press a calculate button.

Try It Now

The full calculator is ready to use above. Decode resistor color codes, look up SMD markings, calculate LED resistors, design voltage dividers, and find standard values — all free, right in your browser.

Common Resistor Values Quick Reference

The most frequently used resistor values in electronics projects are 100Ω, 220Ω, 330Ω, 470Ω, 1kΩ, 2.2kΩ, 4.7kΩ, 10kΩ, 47kΩ, and 100kΩ. These cover most LED current limiting, pull-up and pull-down resistors, voltage dividers, and basic signal conditioning circuits. All of these are available in the E24 standard series in both through-hole and surface mount packages.

When to Use Each Resistor Type

Through-hole resistors with color bands are ideal for breadboard prototyping, through-hole PCBs, and educational projects where you need to identify values visually. SMD (surface mount) resistors are used in production PCBs, compact designs, and any project that needs to minimize board space. For most hobbyist Arduino and ESP8266 projects, ¼W through-hole resistors from the E24 series cover nearly every use case.

Get the Parts

Browse our selection of resistors, LEDs, Arduino and ESP boards, and electronic components for your next project.