I've heard people pronouncing the following 'words' in different ways and I would like to know the correct way of pronouncing them.

  • SPI (spy vs s.p.i)
  • I2C (I.2.C vs I.squared.c)
  • LED (lead vs L.E.D)

I use s.p.i, i.2.c and l.e.d because these are all abbreviations and not really 'words'. I mean, people don't really call USB as us-b right?

  • 5
    \$\begingroup\$ I spell them out as you do, because as you say, they aren't really words. \$\endgroup\$ Feb 13, 2013 at 14:30
  • 1
    \$\begingroup\$ I also spell-out those examples, although strangely I pronounce some abbreviations (eg DIN & DIP) as words as do many other engineers I know. \$\endgroup\$
    – MikeJ-UK
    Feb 13, 2013 at 14:39
  • 1
    \$\begingroup\$ I2C is actually IIC (inter-IC) so i-squared-c is more appropriate than i2c, but I agree on the others. \$\endgroup\$
    – user16324
    Feb 13, 2013 at 14:54
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    \$\begingroup\$ @BrianDrummond the NXP specification says it is either Inter IC or i²c. IIC isn't used. \$\endgroup\$
    – Passerby
    Feb 13, 2013 at 16:26
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    \$\begingroup\$ @Passerby : I'm sorry I was unclear - I did not mean that the IIC written form was valid; I meant to highlight the reason the '2' meant "squared" rather than "two" or even "to". \$\endgroup\$
    – user16324
    Feb 13, 2013 at 16:37

4 Answers 4


I think pronunciation is related to region, laziness and the presence of phonetic pronunciation.

  • Short acronyms are regional - Several answers here indicate this by the variation in SPI pronunciation.

  • Longer acronyms (4 letters or more) are generally pronounced phonetically due to laziness if they have a phonetic pronunciation. Some examples:

Longer acronyms with phonetic pronunciation to some extent

  • UART - Yu - ART
  • ASCII - AS - KEY
  • VHSIC - VEE - H - SIC

Acronyms with no phonetic pronunciation

  • VHDL - VEE - H - DEE - EL
  • XKCD - EX - KAY - CEE - DEE ;)

My pronunciation:

  • SPI - ES - PE - EYE
  • I2C - EYE - squared - C
  • LED - EL - EE - DE
  • USB - YU - ES - BE
  • 2
    \$\begingroup\$ You "My pronunciation" section is what i also use, so have a +1 ;) \$\endgroup\$
    – Rev
    Feb 13, 2013 at 15:51
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    \$\begingroup\$ Yup, exactly what I do. +1 \$\endgroup\$ Feb 13, 2013 at 17:04
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    \$\begingroup\$ Ditto. Er, DIT - TOE. :) \$\endgroup\$ Feb 13, 2013 at 18:01
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    \$\begingroup\$ Also, other protocols like CAN... I never heard any one saying See Ae En! \$\endgroup\$
    – Swanand
    Feb 13, 2013 at 18:54
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    \$\begingroup\$ @Madmanguruman Dude, it's Ditt-Oh. \$\endgroup\$
    – Passerby
    Feb 13, 2013 at 19:47

I2C, SPI, and USB have no set pronunciation. NXP/Phillips, Motorola, and the USB consortium declined to set a pronunciation in the relevant specifications for each of the protocols. They also decline to state whether they are acronyms or abbreviations. As such, there is no set guide for how they should be pronounced or used. It is left to common usage.

Personally, all four are abbreviations, and I pronounce them as such. I2C as Eye Two Cee instead of Eye Squared Cee, though Squared is more accurate. I have heard SPI called the Spy Bus, but not often. And that was a bit conflicting as there is a Spy Bi-Wire bus used by Texas Instruments, normally referred as SBW or Spy.

Basically, you pronounce them like others you talk to pronounce them, and never bring it up in polite conversation.

SPI = "Spy" as in "the Spy Bus" 
I2C = "eye squared sea" as in IIC = I^2 * C = I2C = Inter-Integrated Circuit Bus 
LED = "El Ee Dee" (but Dave Jones does say it like the past tense of "lead" routinely)

There is, of course, no definitive right answer to this question as you'll hear them spoken in different ways by different people. But all the cool kids are saying it this way.

For fun, UART is said "You Art", QUART is said "Queue Art", ARM is said "arm", IC is said "ick" (j/k)

  • 2
    \$\begingroup\$ Dave Jones does pronounce a few things differently, most of which I attribute to an Australian accent. But pronouncing "LED" as a word, I do find annoying. :) \$\endgroup\$
    – JYelton
    Feb 13, 2013 at 17:25
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    \$\begingroup\$ @JYelton, old question that got bumped but reading the answers my first though was huh who spells out LED. Never realised it was a regional thing but everyone in Australia from professionals to LED lighting advertisements pronounce it that way. \$\endgroup\$
    – PeterJ
    Apr 14, 2014 at 21:58
  • \$\begingroup\$ @PeterJ Interesting to know it's not just a peculiarity of Dave's. :) \$\endgroup\$
    – JYelton
    Apr 14, 2014 at 22:00

SPI = Spy

I2C = eye - two - sea

LED = Ell - EEE - DEE

USB = You - Ess - Be


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