Reading the bands, left to right
Resistor color coding exists because printing legible numbers on a component a few millimeters long isn't practical, so the IEC 60062 standard assigns each color a digit, a multiplier, or a tolerance percentage depending on its position. Orientation matters: the tolerance band (usually gold or silver, sometimes brown) is normally spaced slightly apart from the others, and it should end up on your right as you read.
On a standard 4-band resistor, the first two bands are digits 0-9, the third band is the multiplier — including gold meaning ×0.1 and silver meaning ×0.01 for resistors under 10 Ω — and the fourth band is tolerance. So for yellow-violet-red-gold: yellow = 4, violet = 7, red = ×100, gold = ±5%. That gives (4×10 + 7) × 100 = 47 × 100 = 4700 Ω, or 4.7 kΩ, with a manufactured value guaranteed to fall within ±5% of that.
| Band | Color | Meaning | Value |
|---|---|---|---|
| 1st | Yellow | 1st digit | 4 |
| 2nd | Violet | 2nd digit | 7 |
| 3rd | Red | Multiplier | ×100 |
| 4th | Gold | Tolerance | ±5% |
4-band vs 5-band vs 6-band — what changes
A 4-band resistor's two digit bands can only express values like 47, 22, or 68 before the multiplier kicks in — perfectly fine for a ±5% or ±10% part, since the tolerance window is wide enough that finer digit precision wouldn't mean anything. A 5-band resistor, common on ±1% and ±2% parts, adds a third digit band (hundreds-tens-units instead of tens-units), so it can specify values like 499 or 221 that a 4-band code simply can't represent.
A 6-band resistor carries everything a 5-band one does, plus a temperature coefficient (ppm/°C) band at the very end — this matters in precision measurement and calibration circuits where a component's resistance needs to stay stable as it warms up, but it's rarely relevant for hobbyist or general-purpose work.
Tolerance colors and why "odd" values like 4.7k exist
Tolerance also explains why resistor catalogs are full of values like 4.7 kΩ, 2.2 kΩ, or 6.8 kΩ instead of clean round numbers. Manufacturers only produce parts at fixed steps called E-series values (IEC 60063), spaced so each step is roughly one tolerance-band apart from its neighbor — that way no usable value range is left uncovered, and no two adjacent parts are redundant.
E12 (±10% tolerance) has 12 values per decade; E24 (±5%) has 24; E96 (±1%) has 96, spaced much more finely. For example, in E24 the steps around 4-5k are 3.9, 4.3, 4.7, 5.1, 5.6 — there's no 4.5k in that series, which is why you won't find one on a shelf of standard ±5% resistors even though nothing stops someone from wanting exactly 4.5k for a design.
| Value | 4-band code |
|---|---|
| 3.9 kΩ | Orange-White-Red-Gold |
| 4.3 kΩ | Yellow-Orange-Red-Gold |
| 4.7 kΩ | Yellow-Violet-Red-Gold |
| 5.1 kΩ | Green-Brown-Red-Gold |
Going the other direction — from an ohm value to a color code — works by rounding your target value to however many significant digits your chosen band count supports, then expressing the remainder as a multiplier. Typing "4k7" or "2M2" (engineering notation) works the same as typing "4700" or "2200000" directly.
SMD codes: when there are no bands at all
Once resistors get small enough to be soldered directly onto a circuit board (SMD/SMT packages), there's no room to paint multiple color bands legibly, so manufacturers print a short numeric code on the chip's surface instead. The logic is the same idea as color bands — significant digits plus a multiplier — just represented as printed characters. A 3-digit code has 2 significant digits then a multiplier digit; a 4-digit code has 3 significant digits then a multiplier digit, used for the finer resolution ±1% parts often need.
Precision parts sometimes use the EIA-96 system instead, where a 2-digit code (01 through 96) maps to a specific 3-digit significant-value in a published lookup table, followed by a letter that encodes the multiplier — so "01A" isn't read digit-by-digit like 01 and A separately, but as "code 01 → value 100" times the multiplier for A (×1), giving 100 Ω. A "000" or "0" code is a special case meaning a zero-ohm jumper link, not an actual resistance value.
Package size also hints at how much power the part can handle — a hypothetical example: an 0603-size SMD resistor is typically rated around 1/10 W, while a larger 1206-size part in the same series is typically rated around 1/4 W, though exact figures always depend on the manufacturer's datasheet rather than the package code alone.