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Resistor Calculator

Calculate resistance from color codes (4/5 band), series and parallel combinations, and conductor resistance by material and dimensions.

Resistor Color Code

Resistance
51 MΩ
±5% (48.45 MΩ – 53.55 MΩ)

Resistors in Series

Enter values separated by commas

Total (4 resistors)
192 Ω
R = 12 Ω + 47 Ω + 100 Ω + 33 Ω

Resistors in Parallel

Enter values separated by commas

Total (3 resistors)
103.056 Ω
1/R = 1/220 Ω + 1/470 Ω + 1/330 Ω

Conductor Resistance

Resistance (R = L / σA)
267.038 mΩ
2.6704e-1 Ω

Resistor Color Code Chart

ColorDigitMultiplierTolerance
Black0×1—
Brown1×10±1% (F)
Red2×100±2% (G)
Orange3×1K±0.05% (W)
Yellow4×10K±0.02% (P)
Green5×100K±0.5% (D)
Blue6×1M±0.25% (C)
Violet7×10M±0.1% (B)
Grey8×100M±0.01% (L)
White9×1G—
Gold—×0.1±5% (J)
Silver—×0.01±10% (K)

Series vs Parallel Circuits

PropertySeriesParallel
Total ResistanceR₁ + R₂ + R₃1/(1/R₁ + 1/R₂ + 1/R₃)
CurrentSame through allDivides across branches
VoltageDivides across resistorsSame across all
Total vs IndividualAlways largerAlways smaller
If one fails (open)Circuit breaksOthers still work

Conductor Resistance Formula

R = L / (σ × A)

  • R = resistance (ohms, Ω)
  • L = conductor length (meters)
  • σ = conductivity (siemens per meter, S/m)
  • A = cross-sectional area (m²) = π(d/2)²

Conductivity of Common Materials

MaterialConductivity (×10⁶ S/m)Relative to Copper
Silver63.0106%
Copper59.6100%
Gold41.169%
Aluminum37.763%
Brass15.025%
Iron10.317%
Nichrome0.931.6%

Common Resistor Values (E12 Series)

Standard resistor values follow a geometric sequence. The E12 series has 12 values per decade:

1.0, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, 8.2

Multiply by powers of 10: 10Ω, 12Ω, 15Ω ... 1kΩ, 1.2kΩ, 1.5kΩ ... 100kΩ, etc.

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Frequently Asked Questions

How do I read resistor color codes?

Read bands left to right. For 4-band: first two bands are digits, third is multiplier, fourth is tolerance. For 5-band: first three bands are digits, fourth is multiplier, fifth is tolerance. The tolerance band (usually gold/silver) is spaced farther from the others.

What is the difference between 4-band and 5-band resistors?

4-band resistors have 2 significant digits (e.g., 47 × 1K = 47kΩ). 5-band resistors have 3 significant digits for greater precision (e.g., 475 × 100 = 47.5kΩ). 5-band resistors are used in precision applications.

How do series resistors add up?

In series, resistances simply add: R_total = R1 + R2 + R3 + ... The total is always larger than any individual resistor. Current is the same through each resistor, but voltage divides across them.

How do parallel resistors combine?

In parallel: 1/R_total = 1/R1 + 1/R2 + 1/R3 + ... The total is always less than the smallest individual resistor. Voltage is the same across each, but current divides. For two resistors: R_total = (R1 × R2) / (R1 + R2).

What is conductor resistance?

A conductor's resistance depends on length, cross-section area, and material conductivity: R = L / (σ × A). Longer wires have more resistance. Thicker wires have less. Copper conducts better than steel.

What does tolerance mean?

Tolerance is the maximum deviation from the stated value. A 100Ω ±5% resistor can be 95-105Ω. Gold = ±5%, Silver = ±10%, Brown = ±1%. Lower tolerance costs more but is needed for precision circuits.

What is a potentiometer?

A potentiometer is an adjustable resistor with three terminals. Two terminals connect to the full resistance; the third (wiper) slides along the resistive track. Rotating the knob changes the resistance between the wiper and either end.

What is the E24 resistor series?

The E24 series provides 24 standard resistance values per decade, covering a ±5% tolerance range. Common E24 values include 1.0, 1.1, 1.2, 1.3, 1.5, 1.6, 1.8, 2.0, 2.2, 2.4, 2.7, 3.0 — multiply by any power of 10 for the full range.