Convert KB and MB

Convert MB and KB directly

On a desktop, the result appears next to the inputs. On a smartphone, it appears below them. You see it in the selected target unit and also in bytes, MB and MiB. Use “Swap units” to switch the source and target units, for example from converting MB to kB to converting kB to MB. This lets you handle both directions on the same page.

Here is the short answer to the most common question: 1 MB is 1,000 kB. Kilobytes and megabytes are decimal units and increase in steps of a thousand. 1 kB equals 1,000 bytes, and 1 MB equals 1,000,000 bytes. To convert MB to kB, multiply by 1,000. To convert kB to MB, divide by 1,000. The KB option in the calculator's unit list means exactly this decimal kilobyte. If you want to calculate with 1,024, choose the binary units KiB, MiB or GiB.

KB and KiB: Which unit is meant?

There are two ways to count file sizes. The decimal SI units kilobyte, megabyte and gigabyte increase in steps of 1,000. The binary IEC units kibibyte, mebibyte and gibibyte increase in steps of 1,024. The names sound similar, but the byte counts are different, and the gap grows larger with each step.

In a direct comparison, 1 MB has 1,000,000 bytes and 1 MiB has 1,048,576 bytes. A mebibyte is therefore 48,576 bytes larger, which is just under 5 percent. Between GB and GiB, the difference is already around 7.4 percent. Within one system, things stay simple: 1 MB = 1,000 kB and 1 MiB = 1,024 KiB. Problems only start when the two systems are mixed. An equation such as 1 MB = 1,024 kB does not fit either definition.

Is the calculation based on 1,000 or 1,024?

That depends on the unit, not on the calculator. The factor 1,000 applies to kB, MB and GB, and the factor 1,024 applies to KiB, MiB and GiB. It becomes unclear when a size is labeled only “MB” and nothing says which system is meant, because programs and older texts do not all use this abbreviation the same way. So don't assume that your file manager, your email program and the portal you upload to all use the same counting system. The recipient's specification is what counts. If it does not say whether 1,000 or 1,024 is meant, you are on the safe side with the smaller, decimal value. The example in the next section shows why.

An example with a PDF size limit

Suppose an upload form accepts PDFs up to 10 MB, and your file is 10 MiB. Both numbers were chosen for illustration and do not come from any real portal. At first glance, the file seems to fit, since both figures are 10. Working it out in bytes shows otherwise:

1. File in bytes: 10 MiB × 1,048,576 = 10,485,760 bytes.
2. The same byte count in MB: 10,485,760 ÷ 1,000,000 = 10.48576 MB.
3. Limit in bytes: 10 MB × 1,000,000 = 10,000,000 bytes.
4. Comparison: 10,485,760 bytes is 485,760 bytes more than allowed. The file is too large.

Whether you describe the file as 10 MiB or as 10.48576 MB, it still has 10,485,760 bytes, and the limit is still exceeded. The reverse also holds: if you stay below 10,000,000 bytes, you are under a “10 MB” limit in either interpretation, because the decimal interpretation is the stricter one.

The rule of thumb: always convert through bytes

With mixed units, you don't need to memorize a separate factor for each pair, such as one that converts MiB directly to kB. First convert to bytes by multiplying the value by the byte factor of the source unit. Then divide by the byte factor of the target unit. This is exactly how the calculator works: result = value × factor of the source unit ÷ factor of the target unit. For 10 MiB in kB, that means 10 × 1,048,576 ÷ 1,000 = 10,485.76 kB.

You should also keep bits and bytes apart. One byte has 8 bits. This matters mainly for transfer rates, which are usually given in Mbit/s, while file sizes are given in bytes. For this reason, the calculator uses byte units only and offers no bit option. To find out how long an upload takes on your connection, you can calculate the upload time separately.

Entering numbers and understanding rounding

The calculator reads numbers in English notation, as long as they are unambiguous. A period is the decimal separator, and a comma is used only to group thousands, never as a decimal separator. This creates a pitfall that is easy to miss:

• Use a period for decimals: 1.5 means one and a half. A decimal comma is not accepted, so 1,5 is rejected.
• 1.000 with only one period is read as 1, not as one thousand, because the period is the decimal point.
• To enter one thousand, type 1000, 1,000 or 1,000.00. Spaces are not accepted as thousands separators, so 1 000 is rejected.
• The calculator does not accept scientific notation such as 1e6. It also rejects malformed digit grouping, such as dots used as thousands separators (1.000.000), commas that do not separate groups of three digits (12,34,567.89), or doubled commas (1,,234). In those cases, it rejects the input instead of calculating with a misread number. Correctly placed comma separators, as in 1,000,000 or 1,234,567.89, are accepted.
• 0 is allowed. A negative value such as -1 is recognized as a number, but this field does not allow negative values and rejects them.

Results are shown with a decimal point and comma thousands separators, and long decimal places are rounded for display. If you are close to a limit, compare the byte count rather than the rounded MB figure. Very small results stay visible: 1 byte is 0.000000001 GB. Instead of showing a rounded 0, the calculator displays such values in scientific notation, as a power of ten.

There is also an upper limit. If a result is too large to be shown accurately, the calculator rejects the input instead of displaying an inaccurate number. The file sizes involved in uploads and attachments are nowhere near this limit.

File too large? The right next step

If the comparison shows that your PDF is over the limit, converting it further won't help. Switching to another unit does not make the file smaller or sharper. It does not remove any pages, and it does not decide whether a portal accepts the file. A PDF only gets smaller when its byte count actually changes.

• If a single file is over the limit, you can reduce the PDF to a target size. Use the recipient's limit as your target. If it is unclear whether the limit is meant in decimal or binary terms, plan with the smaller decimal value.
• If several conditions apply at once, such as a limit per file and a total limit, you can check your files against upload limits and test them against all values at the same time. That tool reads the actual size of the selected PDFs locally, so you don't have to convert anything by hand.