Kb vs. KB

If you haven’t already read about the difference between bits and bytes, you may want to familiarize yourself with them in part one of this article by clicking here.


KB and Kb are completely different… depending on who you ask!


Kb stands for Kilobit    (1,000 bits)

KB stands for Kilobyte (1,024 Bytes that we often round to 1,000 Bytes.  Or 8,192 bits)


Remember, Bytes are about 8 times larger than bits, so

1,000 Bytes   = 8Kb

100,000 Bytes (97.6 KB*) = 800Kb

1,250,000 Bytes (1.19MB**) = 10Mb


*100,000 Bytes is not equal to 100 KB because 1 KB is 1,024 Bytes.  So you have to divide 100,000KB by 1,024KB to get 97.6KB.

**Same goes for 1,250,000 Bytes.  Divide by 1,024 to get 1,220.70KB, then divide again by 1,024 to get 1.19MB



What is the practical application of such information?   Data streams are measured in bits per second, where file sizes are measure in Bytes.   To make matters worse, file sizes are often “estimated” using prefixes such as Kilo, Mega, and Giga.

(See my article Bits vs Bytes that explains the problem with rounding which is becoming ever greater as we get to Tera and Peta prefixes)


When we save a file, we save it in Bytes, but if we want to play it online, it streams or downloads in bits per second.  Sometimes you may hear someone say they want a video file to play the “highest quality possible.”    Well, the operative word here is “possible.”   What is possible is constantly changing, and is quite subjective.


Let’s say you have a file that is 10MB in size.   How long would it take to download?  Let’s say you can download a file at 20Mbps.  That does NOT mean it will take half a second.  10MegaBytes is approximately 80Megabits.  In theory, that means it would take 4 seconds.  However, that’s in perfect conditions.  In reality, you’ll still be at the mercy of the “upload” speeds of the server you access.


For example, my office computer just tested download speeds at 36Mbps.  Pretty impressive.   I just downloaded a 6MB file (that’s 48megabits) and it took 5.5 seconds instead of about  1.25 seconds.  My home computer tested download speeds at 17Mbps.  That same file from the same website took 10 seconds to download instead of 3 seconds.   So, we’re just not in a perfect world.


So, how do you know what size you should use for saving video files for online streaming?  For now (note the date of this article), 800-1200kbps seems to be a safe average range.   If you target a data rate of 800kbps, that means your file size would be approximately 100KB (800kb / 8 = 100KB) per second of video.  So a one minute video should not be too much larger than 6MB (100KB * 60 seconds = 6,000KB… or about 6MB). This is not exact because this does not account for compression at variable bit rates, but it’s a safe place to start.


The rest of this is just anecdotal, but how does all of this compare to dial up speeds a few years back?  Remember 56k modems?   Well 56kb is only 7 KiloBytes of data per second.  That means in that perfect world (which we’ve shown doesn’t exist), it would take over 14 minutes to download that same 6MB file.   In reality, we typically had connection speeds around 12kbps, and a god-forsaken huge 6MB file took over an hour!  Compare today’s 5 seconds to 4,000 seconds just 10 years ago!