What do you want to know, and which values do you have?
Each calculator answers a specific question. You'll find the right one fastest by starting from two things: what you want to know in the end and which values you already have.
Formulas, worked examples and notes on rounding are on each calculator's own page.
File size, print size, upload time or limit?
The question “How big is my PDF?” can mean very different things. The word “size” covers four different things, and each one has its own calculator:
- File size: how much storage the file takes up, measured in bytes, KB, MB or MiB. This is what unit conversion, the compression rate and the email estimate are about.
- Print size and image resolution: how large an image will be on paper, measured in centimeters, pixels and PPI. The DPI calculator works this out.
- Upload time: how many seconds or minutes a transfer takes at a given upload rate.
- Upload limit: whether your files meet a requirement, such as a maximum size per file, a total size, a number of files or a page count.
Print size and file size cannot be converted into each other. An image with 3,000 × 2,000 pixels mathematically yields a print size of about 25.4 × 16.93 cm at 300 PPI. How many megabytes a PDF containing this image has does not follow from that, because the byte count depends on how images and content are stored in the file. For questions about print format, the DPI calculator is therefore the right one; for questions about megabytes and limits, use the unit calculator or the limit calculator.
A second example with assumed values: A portal allows 10 MB per PDF and 20 MB in total. Here the upload limit check helps you, not the upload time or the email estimate. If a file is over the limit, the next step is to actually compress the PDF.
Calculate, check locally or change a PDF
For five of the six calculators, you don't need a file. You only enter numbers, such as a size, an upload rate or pixel dimensions. The exception is the upload limit check: there you can enter sizes and page counts manually or select PDFs on your device. The calculator then reads the file size and, for supported PDFs, the page count. The files are neither sent to a portal nor changed in the process.
So selecting files in the calculator is not an upload to the recipient. You do the actual upload yourself later, in the portal or in your email program.
When the file really needs to get smaller
No calculator compresses, splits or sends a PDF. The result is always a number or a check status. The compression calculator only calculates, too: it shows you how much a reduction achieved or how much is still missing, but it doesn't change any file.
If a calculator shows you that a file is too large, switch to a tool that creates a new file. For a smaller file, you can compress the PDF. If you'd rather remove pages, split a file or merge several PDFs, you can view the PDF tools. You can then check the saved result again with the calculators.
Use results with their assumptions
How far you can rely on a result depends on what is being calculated. Some values are pure math; others rest on assumptions you set yourself.
- Units: Conversions follow fixed factors, for example 1 MB = 1,000,000 bytes and 1 MiB = 1,048,576 bytes. Displayed values may be rounded. Enter decimals with a period, for example 1.5; a decimal comma such as 1,5 is not accepted.
- Print dimensions: The geometry is correct for the entered pixels and the chosen PPI. The number alone doesn't tell you whether the print will look sharp enough.
- Email: The message size is an estimate based on Base64 encoding and the additional settings you choose. It shows whether things are getting tight, but it is not proof that the email will arrive. More on this in the guide Compress a PDF for email.
- Upload time: The calculator works with the upload rate and efficiency you specify. It doesn't measure your connection.
- Limits: The check only compares the limits you enter. The recipient still decides on format, completeness, legibility and acceptance of your documents.
Which assumptions a calculator uses exactly, and how to set them, is explained on each calculator page right next to the input fields.