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I've seen some circuit diagrams on-line that appear to use the units prefix symbol as the decimal point. So a 6.8kΩ resistor is shown as 6k8 and a 1.2nF capacitor is shown as 1n2. Is this an accepted practice, and am I interpreting the values correctly?

Annette Gates
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  • Both of them are representing the same values and yes, accepted. – OJazz May 17 '22 at 14:36
  • Related/duplicate: https://electronics.stackexchange.com/q/107698/2028, https://electronics.stackexchange.com/q/28053/2028, https://electronics.stackexchange.com/q/246920/2028 – JYelton May 17 '22 at 16:08
  • I've written a little python library that generates and parses this type of string. – Neil_UK May 17 '22 at 18:19
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    Note that this is even accepted/common practice enough to be supported by many tool like circuit designers or simulators as input format. – PlasmaHH May 18 '22 at 10:06
  • Also, some components also have markings in this format. I think I've first seen it on '70-'80 era soviet resistors. It's an intuitive notation in my opinion. – Uncle Dino May 19 '22 at 12:19

2 Answers2

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Yes, the practice is certainly accepted although there may not be a formal standard or requirement. You are interpreting the values correctly. Note that when no prefix is needed we use the quantity symbol instead, so \$1.1\Omega\$ is written as 1R1.

Elliot Alderson
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    Sometimes R is used even when it's not a resistor, though. I've seen it used for inductors too. – Hearth May 17 '22 at 14:50
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    @Hearth - You've actually see this for ferrite beads, I would think. They are typically referred to by their impedance (say, 100R) over a certain frequency range. Actual inductors will be marked in Henrys. – SiHa May 18 '22 at 06:08
  • is it always the quantity symbol? would you write 1H1 or 1L1? hopefully your diagram does not include a current source – user253751 May 18 '22 at 09:19
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    Using R instead of Ω comes from the fact that Ω may not be available in the typeset or on the keyboard or in the character encoding. These conventions predate unicode. – Rodney May 18 '22 at 10:06
  • If for resistance we can have 100R, and say 1R1, then it follows that for inductance because we use H (100H, 100nH) then we would use 1H1. Though an inductance that big is likely not to be even that precise, just 1H probably. – Rodney May 18 '22 at 10:08
  • @Rodney No, don't confuse the symbol for the **quantity** (L for inductance) with the symbol for its SI **unit** (H for henries). – Elliot Alderson May 18 '22 at 10:11
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    @ElliotAlderson I have never seen a 100nH inductor labelled as 100nL on a schematic, it's either 100nH or 100n. So it's always the unit, or nothing. So we would expect H as the decimal point substitute, 1H1 not 1L1. (Resistance is different because it's a special case of avoiding the Ω symbol.) – Rodney May 18 '22 at 10:24
  • @SiHa No, I've definitely seen R as the decimal point substitute for inductors. In part numbers and part markings, mostly--look for instance at the Bourns part number [SRR4028-3R3Y](https://www.digikey.com/en/products/detail/bourns-inc/SRR4028-3R3Y/1970240), a 3.3 μH inductor (the base unit for inductor codes is μH). – Hearth May 18 '22 at 14:13
  • @Hearth - Good point. Now that I've seen those, I realise that I've seen it before, as well. My mistake. – SiHa May 18 '22 at 15:11
  • @Rodney: I think the conventions predate any form of computerized schematic entry. Many lettering templates don't have an "Ω" character, and even if they did, a value written as 33Ω would be much more likely to be mistaken for 330 (ohms), or vice versa, than would values written as 33R or 330R, and 3.3 would be much more likely to be mistaken for 33, or vice versa, than values written as 33R or 3R3. – supercat May 18 '22 at 16:45
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This improves the readability of printed values on components. A decimal point may be overlooked or is just missing on bad printing quality. You can even find this practice on schematics, BOMS and components, that are 50+ years old. If you see 470 printed on a capacitor the value is not 470pF! You must read it in the code of the color rings on resistors: 4, 7 and no zero digits behind. It's 47pF then, 471 would be 470pF and 475 is 4.7uF. The same on inductors: 101 is 100uH, R27 is 270nH. Using R on an inductor is absurd but very common.

Jens
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