To get a sharp print, your file must have a minimal resolution. The minimum resolution for printing is usually 300 DPI (dots per inch). For very large-sized printing 150 DPI will do. Do you use a lower resolution than indicated? Then you have a chance that your image will be unsharp/blurry.
Formula to calculate file dimensions from pixels
You already have your file, but you want to know the maximum print size.
Go to the properties of the file. Here you find the dimensions in pixels. Using the formula below, you can derive the biggest printable size from the number of pixels.
amount of pixels / 300 DPI x 2,54 = maximum file size in cm
Formula to calculate amount of pixels from file dimensions
If you would like to know how many pixels a file should have for it to be printed in a certain size, you can use the formula below.
size in cm / 2,54 x 300 DPI = amount of pixels
Example: You want to print a flyer on A3 sizing (2,97 x 4,20 cm).
2,97 / 2,54 x 300 = 351
4,20 / 2,54 x 300 = 496
So the file for the A3 flyer should have a minimum of 351 x 496 pixels.
Please note: This formula is a theoretic calculation and will not always result in the correct dimensions. If the photo was taken in the dark, is overexposed or blurred by motion, the resolution will be sufficient but the quality may be inadequate.