One megabyte is 1,000 kilobytes decimally, so a kilobyte is 0.001 MB. Of all the storage prefixes this is the one where the binary alternative causes least trouble, because the 2.4 per cent gap at this step is small enough to disappear into rounding.
About the units
The kilobyte was the first storage prefix to be widely used and the first to be misapplied: early computing adopted 1,024 bytes because 2¹⁰ is close to a thousand and the binary value fell naturally out of memory addressing. The lowercase k in the SI system means a thousand, and an uppercase K was sometimes used for the binary value, but the convention was never consistent. The IEC settled it in 1998 with kibibyte, KiB, for 1,024 bytes. Older documentation is unreliable on which is meant, and for kilobyte-scale files the difference rarely matters enough for anyone to check.
The exact factor
The factor is 1,000 decimal, 1,024 binary. At this scale the two differ by 24 bytes in a thousand, which is why a text file listed as 47 kB is described the same way by almost every tool regardless of convention. The divergence only becomes practically important two prefixes up. Worth noting alongside: a kilobyte is 8,000 bits, so a file size in kilobytes multiplied by eight gives the bits that must cross a connection to transfer it.
Where you meet this conversion
Source code, configuration files, plain text and web assets. Web performance work lives at this scale: an HTML document is tens of kilobytes, a stylesheet or script often hundreds, and page weight budgets are set in kilobytes precisely because the megabyte is too coarse to argue about. Font files, favicons and compressed images are all specified here. Email systems still enforce limits in this range for individual message headers and inline content.