5.1 MΩ resistor colour code
greenbrowngreengold
5.1 MΩ ±5%
green brown green gold — four bands, read from the end with the bands closest to it.
| Band 1 — first digit | green = 5 |
| Band 2 — second digit | brown = 1 |
| Band 3 — multiplier | green × 100,000 |
| Band 4 — tolerance | gold ± 5% |
| Value | 5.1 MΩ |
| Acceptable range | 4.84 MΩ to 5.36 MΩ |
Reading it
The two digit bands give 51 and the multiplier band multiplies it by 100,000:
51 × 100,000 = 5.1 MΩ
Which end to start from is the part that catches people. The tolerance band is the one set slightly apart from the other three, and it is gold or silver far more often than not — neither of which is a digit colour, so a gold or silver band tells you which end you are at. Read from the opposite end.
What ±5% actually means
A 5.1 MΩ ±5% resistor is in specification anywhere from 4.84 MΩ to 5.36 MΩ. A meter reading of 4.84 MΩ on this part is not a fault and not a reason to replace it.
5.1 MΩ is one of the E24 values — the 24 steps per decade that ±5% resistors are made in. The steps are spaced so that the tolerance bands of neighbouring values just about touch: there is no gap between one value's range and the next, and no point making anything in between. It is the same reasoning that gives ±10% parts only 12 values per decade.
The same resistor with five bands
Precision resistors carry five bands: three digits, a multiplier and a tighter tolerance. The same 5.1 MΩ reads
greenbrownblackyellowbrown
— green brown black yellow brown. The digits become 5, 1 and 0, and the multiplier drops one decade to yellow to compensate. The brown final band is ±1% rather than ±5%, which narrows the range to 5.05 MΩ–5.15 MΩ.
How much this one can take
A resistor's limit is heat, not voltage or current on their own: the power it turns into heat is V² ÷ R, so the same wattage allows very different numbers at 5.1 MΩ than it does at a value ten times away. This is the part of a colour code lookup people actually came for and charts leave out.
| Rating | Maximum current | Maximum voltage |
|---|---|---|
| ⅛ W | 157 µA | 798.4 V |
| ¼ W | 221 µA | 1129.2 V |
| ½ W | 313 µA | 1596.9 V |
| 1 W | 443 µA | 2258.3 V |
The quarter-watt part is the one in everybody's drawer: at 5.1 MΩ it will carry 221 µA or stand 1129.2 V across it, and not both at once — those are the same limit expressed two ways.
5.1 MΩ exists only at ±5%
5.1 MΩ is an E24 value that is not in the E12 series, so it is made at ±5% and tighter but not at ±10%. That is why it is missing from cheap assortment boxes, which are usually E12 only — and why a design that calls for 5.1 MΩ is harder to service from a beginner's drawer than one that calls for 4.7 MΩ.
The nearest E12 value is 4.7 MΩ, 7.8% away, which is inside the ±5% band of neither part but close enough to substitute in most non-critical positions.
The same resistor as a surface-mount marking
Surface-mount resistors have no room for bands, so they carry printed digits instead — and 515 is what 5.1 MΩ looks like on one. The scheme is the colour code with the colours replaced by the digits they stood for: two significant figures and a count of zeros.
| Marking | Used on | Reads as |
|---|---|---|
515 | Three-digit, ±5% parts | 51 followed by 5 zeros |
5104 | Four-digit, ±1% parts | 510 followed by 4 zeros |
A four-digit marking is not a different system, only a more precise one: it carries three significant figures instead of two and takes one off the zero count, which is why 515 and 5104 are the same 5.1 MΩ. If a board has both on it, the four-digit parts are the ±1% ones.
Very small ±1% parts use a third scheme, EIA-96, where two digits index a table of values and a letter gives the multiplier — 01C rather than 1002. It only covers the E96 series, so it has no marking for most of the E24 values on this site, and a marking with a letter in the middle is never one of these codes.
Where 5.1 MΩ turns up
Megohm values are for very slow timing, for bleeding charge off a capacitor after power-down, and for keeping a high-impedance input from floating. Currents here are in microamps, so the resistor dissipates almost nothing and the limiting factor is the voltage across it rather than the heat in it.
Frequently asked questions
What is the colour code for a 5.1 MΩ resistor?
green brown green gold on a four-band resistor: green for 5, brown for 1, green for a multiplier of ×100,000, and gold for ±5%.
What resistor is green brown green gold?
5.1 MΩ, ±5%. The first two bands are the digits 5 and 1, the third multiplies by 100,000, and the gold band is the tolerance.
What is the tolerance range of a 5.1 MΩ ±5% resistor?
4.84 MΩ to 5.36 MΩ. A resistor measuring anywhere in that range is within specification, which is why a meter reading of 4.84 MΩ on a 5.1 MΩ part is not a fault.
What is the five-band code for 5.1 MΩ?
green brown black yellow brown — three digit bands (5, 1, 0), then yellow as the multiplier and brown for ±1%. Five-band resistors carry an extra significant figure, so the third digit is the zero that a four-band code leaves to the multiplier.
Nearby values
- 5.6 MΩ resistor colour code — green blue green gold
- 6.2 MΩ resistor colour code — blue red green gold
- 6.8 MΩ resistor colour code — blue grey green gold
- 7.5 MΩ resistor colour code — violet green green gold
- 8.2 MΩ resistor colour code — grey red green gold
- 9.1 MΩ resistor colour code — white brown green gold
- 1 Ω resistor colour code — brown black gold gold
- 1.1 Ω resistor colour code — brown brown gold gold
- 1.2 Ω resistor colour code — brown red gold gold
- 1.3 Ω resistor colour code — brown orange gold gold