How do you read resistor color codes?

Resistors use colored bands to indicate their value. For a 4-band resistor: Band 1 and 2 are significant digits, Band 3 is the multiplier, Band 4 is the tolerance. Read left to right, with tolerance band (usually gold or silver) on the right. Example: Red-Red-Orange-Gold = 22 × 1,000 = 22,000Ω = 22kΩ ±5%. For 5-band resistors, Bands 1, 2, and 3 are digits, Band 4 is multiplier, Band 5 is tolerance.

How do you calculate resistors in series?

For resistors in series, the total resistance is simply the sum: Rtotal = R1 + R2 + R3 + ... + Rn. The same current flows through each resistor, and the voltages across each resistor add up to the total supply voltage. Example: 100Ω + 220Ω + 470Ω = 790Ω total.

How do you calculate resistors in parallel?

For resistors in parallel: 1/Rtotal = 1/R1 + 1/R2 + 1/R3 + ... The equivalent resistance is always less than the smallest individual resistor. For two resistors: Rtotal = (R1 × R2) / (R1 + R2). Example: 100Ω and 100Ω in parallel = 50Ω. Adding more parallel paths gives current more ways to flow, reducing total resistance.

Ohm's Law states that voltage (V) equals current (I) times resistance (R): V = I × R. From this: I = V/R and R = V/I. Power (P) = V × I = I² × R = V²/R. These four relationships form the foundation of circuit analysis. Knowing any two values (V, I, R, or P), you can calculate the other two.

How do you calculate the resistor for an LED?

LED resistor formula: R = (Vsupply − Vforward) / Iled. Where Vsupply is the supply voltage, Vforward is the LED's forward voltage (typically 2.0V for red, 2.1V for yellow/green, 3.0–3.4V for blue/white), and Iled is the desired LED current (typically 10–20mA). Example: 5V supply, red LED (Vf=2.0V), 15mA current: R = (5 − 2.0) / 0.015 = 200Ω.

What does the gold or silver band on a resistor mean?

The gold or silver band indicates the resistor's tolerance — the allowable deviation from the stated value. Gold = ±5% tolerance (most common). Silver = ±10% tolerance. If there is no 4th band, tolerance is ±20%. For 5-band resistors, the 5th band shows tolerance: Brown=±1%, Red=±2%, Gold=±5%. Tolerance bands are usually wider and placed on the right side of the resistor.

What is the E12 and E24 series of resistors?

E-series are standardized resistor values that cover the full resistance range with evenly spaced steps on a logarithmic scale. E12 has 12 values per decade: 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82. E24 has 24 values per decade and is the most common for ±5% resistors. E96 (96 values/decade) is for precision ±1% resistors. These values are multiplied by powers of 10 to cover 1Ω to 10MΩ.

What is the color for 0 through 9 in resistor color codes?

The resistor color code: Black=0, Brown=1, Red=2, Orange=3, Yellow=4, Green=5, Blue=6, Violet=7, Grey=8, White=9. Mnemonic: 'BB ROY of Great Britain Very Good Wife' or 'Bad Boys Race Our Young Girls But Violet Generally Wins'. For multipliers: Gold=×0.1, Silver=×0.01.

Why do resistors have standard color coding?

Resistors are too small to print numbers on legibly, so color bands were adopted as a standardized marking system (IEC 60062 standard). The system allows the value to be read at any orientation and remains readable after soldering. Color coding was introduced in the 1920s and is still universal today. Modern surface-mount resistors (SMD) are too tiny for color bands and use a 3 or 4 digit numerical code instead.

Color Codes · Series · Parallel · LED

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Q: What is the difference between resistance and impedance?

Resistance (R) is the opposition to current flow in DC circuits, measured in ohms (Ω). It is frequency-independent. Impedance (Z) is the total opposition to current flow in AC circuits, combining resistance (R) and reactance (X) from capacitors and inductors. Z = √(R² + X²). For purely resistive circuits (no capacitors or inductors), impedance equals resistance. Resistors have the same value in both DC and AC circuits.

Decode 4 and 5-band resistor color codes, calculate series and parallel resistance, solve Ohm's Law, and find LED current-limiting resistors — all in one tool.

4+5

Band decoder

S+P

Series+Parallel

Ohm

V=IR solver

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R_total = R₁ + R₂ + R₃ + ...

1/R_total = 1/R₁ + 1/R₂ + 1/R₃ + ...

R = (V_supply − V_forward) / I_LED

LED Type sets typical forward voltage

Supply Voltage

Forward Voltage (Vf) from LED type

Desired LED Current

Color Code Reference

Resistor Color Code Chart

Standard IEC 60062 color code. Bands read left to right; tolerance band is on the right.

Color	Digit (Band 1–3)	Multiplier	Tolerance	Temp Coeff (ppm/°C)
Black	0	×1	—	250
Brown	1	×10	±1%	100
Red	2	×100	±2%	50
Orange	3	×1,000	—	15
Yellow	4	×10,000	—	25
Green	5	×100,000	±0.5%	20
Blue	6	×1,000,000	±0.25%	10
Violet	7	×10,000,000	±0.1%	5
Grey	8	×100,000,000	±0.05%	1
White	9	×1,000,000,000	—	—
Gold	—	×0.1	±5%	—
Silver	—	×0.01	±10%	—
None	—	—	±20%	—

Standard Values

E12 Series — 12 Values per Decade

Most common for ±5% resistors. Multiply by 1, 10, 100, 1k, 10k, 100k, 1M for full range.

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Mnemonic for Resistor Color Codes

The classic memory aid: "Bad Boys Race Our Young Girls But Violet Generally Wins" (Black=0, Brown=1, Red=2, Orange=3, Yellow=4, Green=5, Blue=6, Violet=7, Grey=8, White=9). Or simply remember the rainbow: black before colors, then ROYGBIV from 2–8, then white=9, with gold/silver as ±5%/±10% tolerance bands.

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Series vs Parallel

Series: R_total = R1 + R2 + ... Same current flows through all. Total voltage splits across resistors. Total resistance always increases.

Parallel: 1/R_total = 1/R1 + 1/R2 + ... Same voltage across all. Current splits between resistors. Total resistance always less than smallest resistor. Two equal resistors in parallel = half the resistance.

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LED Current & Brightness

LEDs are current-driven devices — without a current-limiting resistor, current increases until the LED burns out. Standard LEDs run at 10–20 mA. The resistor drops (V_supply − V_forward) volts.

Forward voltage (Vf) varies by LED color: red ≈ 2.0V, yellow/green ≈ 2.1V, blue/white ≈ 3.2V. Running at 10 mA instead of 20 mA reduces brightness but greatly extends LED lifetime.

Resistor Formulas — Color Code, Series, Parallel & LED

4-Band Color Code Reading

Band 1 (digit 1) × 10 + Band 2 (digit 2) × Multiplier (Band 3) Tolerance = Band 4 Example: Red - Red - Orange - Gold Band 1: Red = 2 Band 2: Red = 2 Band 3: Orange = ×1,000 Band 4: Gold = ±5% Value: 22 × 1,000 = 22,000 Ω = 22 kΩ ±5%

5-Band Color Code Reading

Bands 1–3 are digits, Band 4 is multiplier, Band 5 is tolerance Example: Brown - Black - Black - Red - Brown Band 1: Brown = 1 Band 2: Black = 0 Band 3: Black = 0 Band 4: Red = ×100 Band 5: Brown = ±1% Value: 100 × 100 = 10,000 Ω = 10 kΩ ±1%

Series & Parallel Resistance

Series: R_total = R1 + R2 + R3 + ... + Rn Parallel: 1/R_total = 1/R1 + 1/R2 + ... + 1/Rn R_total = 1 / (1/R1 + 1/R2 + ... + 1/Rn) Two resistors in parallel shortcut: R_total = (R1 × R2) / (R1 + R2) Example: 100Ω ‖ 150Ω = (100×150)/(100+150) = 15000/250 = 60Ω

Ohm's Law & Power

V = I × R (Voltage = Current × Resistance) I = V / R (Current = Voltage / Resistance) R = V / I (Resistance = Voltage / Current) P = V × I (Power = Voltage × Current) P = I² × R (Power = Current² × Resistance) P = V² / R (Power = Voltage² / Resistance) Units: V (volts), I (amperes), R (ohms Ω), P (watts W)

LED Resistor Formula

R = (V_supply − V_forward) / I_LED V_forward (typical): Red=2.0V, Yellow=2.1V, Green=2.2V, Blue=3.2V, White=3.2V, IR=1.2V I_LED (typical): 10–20 mA (0.010–0.020 A) Example: 5V supply, white LED (Vf=3.2V), 15 mA: R = (5.0 − 3.2) / 0.015 = 1.8 / 0.015 = 120 Ω Power dissipated = (5.0−3.2) × 0.015 = 27 mW Use nearest standard E12: 120 Ω ✓

Frequently Asked Questions

4-band: Band 1 = first digit, Band 2 = second digit, Band 3 = multiplier, Band 4 = tolerance. Read left to right; tolerance band (gold/silver) is on the right. Red-Red-Orange-Gold = 22,000Ω = 22kΩ ±5%. 5-band: Bands 1,2,3 = digits, Band 4 = multiplier, Band 5 = tolerance. Use our Color Code tab above — select each band color and get the value instantly.

R_total = R1 + R2 + R3 + ... Simply add all resistance values. 100Ω + 220Ω + 470Ω = 790Ω. The same current flows through all series resistors; voltages add up. Use Panel 2 above to add as many resistors as needed. Tip: in series, total resistance is always greater than any individual resistor.

1/R_total = 1/R1 + 1/R2 + ... (then take reciprocal). Two-resistor shortcut: R = (R1×R2)/(R1+R2). Example: 100Ω ‖ 150Ω = 15,000/250 = 60Ω. The same voltage appears across all parallel resistors; current splits. In parallel, total resistance is always less than the smallest individual resistor.

V = I × R. Voltage equals current times resistance. Rearranged: I = V/R and R = V/I. Power: P = V×I = I²R = V²/R. Knowing any two of V, I, R lets you find the third. Example: 12V across 100Ω → I = 12/100 = 0.12A = 120mA. Power = 12 × 0.12 = 1.44W → use at least a 2W resistor.

R = (V_supply − V_forward) / I_LED. Example: 5V supply, red LED (Vf=2.0V), 15mA: R = (5−2)/0.015 = 200Ω. Choose nearest standard value (E12): 220Ω. Without a resistor, LEDs burn out instantly from excess current. Forward voltage varies by color: red≈2.0V, yellow≈2.1V, blue/white≈3.2V. Use Panel 4 above for instant calculation.

The last band indicates tolerance — how much the actual value can deviate from the marked value. Gold = ±5% (most common in general circuits). Silver = ±10%. No band = ±20%. For precision circuits, 1% (brown 5th band) or better is needed. A 1kΩ ±5% resistor is guaranteed to be between 950Ω and 1,050Ω.

E-series are standardized resistor values covering the full range with logarithmically spaced steps. E12 has 12 values per decade (for ±10% resistors): 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82. E24 has 24 values (for ±5%). E96 has 96 values (for ±1%). These values × powers of 10 cover 1Ω to 10MΩ. Choosing E-series values ensures you can always buy the exact resistor needed.

Black=0, Brown=1, Red=2, Orange=3, Yellow=4, Green=5, Blue=6, Violet=7, Grey=8, White=9. Mnemonic: "Bad Boys Race Our Young Girls But Violet Generally Wins." Gold and Silver are only used as multipliers (×0.1, ×0.01) and tolerance bands (±5%, ±10%), never as digit bands.

Resistance (R) is frequency-independent opposition to current in DC circuits. Impedance (Z) is the total opposition in AC circuits, combining resistance (R) and reactance (X) from capacitors and inductors: Z = √(R² + X²). Pure resistors have Z = R at all frequencies. Capacitors and inductors have frequency-dependent reactance. For pure resistor circuits, resistance and impedance are equal.

Resistors are too small to print numbers on legibly. Color bands (IEC 60062 standard) allow values to be read at any orientation after soldering. The system was introduced in the 1920s and remains universal for through-hole resistors. Modern surface-mount (SMD) resistors use a 3 or 4 digit code (e.g., "103" = 10,000Ω = 10kΩ) because they're too small even for color bands.

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