A 4-band resistor has bands that encode: 1st digit, 2nd digit, multiplier, and tolerance. The first two bands represent the significant digits of the resistance value. The third band is the multiplier (power of 10). The fourth band indicates the tolerance (accuracy) of the resistor. For example: Yellow (4), Violet (7), Red (×100), Gold (±5%) = 47 × 100 = 4,700 Ω or 4.7 kΩ ±5%. Always orient the resistor so the tolerance band (often gold or silver) is on the right side.

A 5-band resistor provides higher precision with 3 significant digits instead of 2. The bands encode: 1st digit, 2nd digit, 3rd digit, multiplier, and tolerance. This allows for more precise resistance values, commonly found in 1% tolerance resistors. Example: Brown (1), Black (0), Black (0), Red (×100), Brown (±1%) = 100 × 100 = 10,000 Ω or 10 kΩ ±1%.

The 6th band indicates the temperature coefficient (tempco), measured in ppm/°C (parts per million per degree Celsius). This tells you how much the resistance value changes with temperature. A lower ppm value means better temperature stability. Common tempco values: Brown = 100 ppm/°C, Red = 50 ppm/°C, Orange = 15 ppm/°C, Yellow = 25 ppm/°C, Blue = 10 ppm/°C, Violet = 5 ppm/°C. 6-band resistors are typically used in precision applications where temperature stability is critical.

Tolerance indicates the acceptable deviation from the nominal resistance value. Common tolerances: ±1% (Brown), ±2% (Red), ±0.5% (Green), ±0.25% (Blue), ±0.1% (Violet), ±5% (Gold), ±10% (Silver), ±20% (no band). A 1kΩ ±5% resistor can actually measure anywhere between 950 Ω and 1,050 Ω. For precision circuits, use 1% or better tolerance resistors.

A popular mnemonic is: "Better Be Right Or Your Great Big Venture Goes West" — representing Black (0), Brown (1), Red (2), Orange (3), Yellow (4), Green (5), Blue (6), Violet (7), Gray (8), White (9). Another classic: "Bad Boys Race Our Young Girls But Violet Gives Wins." For multiplier and tolerance, remember Gold = 0.1 and Silver = 0.01 for multipliers, and Gold = 5%, Silver = 10% for tolerance.

A 3-band resistor is essentially a 4-band resistor without a tolerance band, which defaults to ±20% tolerance. These are older, less precise resistors. Today, most resistors use at least 4 bands, with 5-band and 6-band being common for precision applications. If you encounter a 3-band resistor, simply read it as a 4-band with no tolerance band (meaning ±20%).

Standard resistor values follow the E-series (E6, E12, E24, E48, E96, E192), which define preferred numbers for each tolerance class. E12 (±10%): 1.0, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, 8.2. E24 (±5%): adds 1.1, 1.3, 1.6, 2.0, 2.4, 3.0, 3.6, 4.3, 5.1, 6.2, 7.5, 9.1. These values repeat for each decade (×1, ×10, ×100, ×1k, ×10k, ×100k, ×1M, etc.). Our calculator displays the exact value — you can compare it against E-series tables to find the nearest standard value.

The main difference is precision. 4-band resistors typically offer ±2%, ±5%, or ±10% tolerance with 2 significant digits. 5-band resistors provide ±1% or better tolerance with 3 significant digits, allowing for more exact values like 10.5 kΩ or 47.5 Ω. In circuit design, use 5-band (or 6-band) when you need precise resistance values, and 4-band for general-purpose applications where exact values are less critical.