There are two kinds of kilobyte. In decimal units 1 kB is 1,000 bytes and 1 MB is 1,000,000 bytes; in binary units 1 KiB is 1,024 bytes and 1 MiB is 1,048,576. Windows shows binary sizes labelled KB, while macOS shows decimal. Enter any size below to see both.
| Decimal unit | Bytes | Binary unit | Bytes (binary) |
|---|---|---|---|
| 1 kB | 1,000 | 1 KiB | 1,024 |
| 1 MB | 1,000,000 | 1 MiB | 1,048,576 |
| 1 GB | 1,000,000,000 | 1 GiB | 1,073,741,824 |
| 1 TB | 10^12 | 1 TiB | 1,099,511,627,776 |
Updated
A converter that shows every unit at once, a box that reads the exact size of any file you drop on it (the file stays on your device), and a page weight calculator for checking a web page against a budget.
| Profile | Megabits per second |
|---|---|
| Weak mobile signal (0.4 Mbps) | 0.4 |
| Patchy mobile data (1.6 Mbps) | 1.6 |
| Decent mobile data (10 Mbps) | 10 |
| Broadband (50 Mbps) | 50 |
Computer memory comes in powers of two, so early software rounded 1,024 bytes to a kilobyte. Everywhere else in science, kilo means exactly 1,000. To clear up the mix, the IEC introduced kibi, mebi and gibi for the powers of two, written KiB, MiB and GiB. Network speeds, drive capacities and most cloud pricing use the decimal units.
The gap grows with each step: about 2.4% at kilo, about 4.9% at mega and about 7.4% at giga. That is why the difference is easy to ignore for a photo and hard to ignore for a hard drive.
A budget turns speed from an opinion into a number that a team can check. Write down a ceiling for each type, for example 150 kB of JavaScript and 600 kB of images, and look at the total before every launch.
The download times in the calculator are the bare transfer time at the given speed. Real loads take longer because of connection setup, round trips and the time the device spends running scripts, so treat them as a lower bound.
Both are in use. Under the SI standard, 1 MB is 1,000 kB. Under the binary convention that Windows and many older programs use, a megabyte means 1,024 kilobytes, which the IEC standard names a mebibyte (MiB). The tool shows both so you can match whichever the other system uses.
Drive makers count in decimal: a 1 TB drive holds 10^12 bytes. Windows divides by 1,024 three times and labels the result GB, so the same drive shows as about 931 GB. No space is missing; it is the same number in a different unit.
No. Browsers block a page from downloading another site's files for security reasons, so an honest in-browser tool cannot do that. Open the page, press F12, reload with the Network panel open and copy the transferred totals into the calculator here. That gives a more accurate figure anyway, because it reflects your real connection, cache and compression.
There is no official limit. Set a budget that suits your audience: a landing page that loads on a mid-range phone on mobile data should be far lighter than an internal dashboard. As a starting point, about 1 MB transferred is a reasonable ceiling for a marketing page; tighten it from there.
Related: Image compressor, PNG to WebP converter, Image to Base64, How to speed up a website, Website grader.
Start for free or see all free tools. We.Inc is free to start, with no card needed. AI building is on paid plans from $20 a month.
We.Inc is an AI-powered website builder you can resell under your own brand. Launch a branded client dashboard, bill on Stripe Connect, and deliver AI-generated websites in minutes. White-label plans start at $99 a month for 25 client sites, with a 7-day free trial and no per-site fees.