The calculation
Width in inches equals pixel width divided by pixels per inch. Height uses the same calculation. Multiply inches by 2.54 to obtain centimetres. For example, an image measuring 2,400 by 1,600 pixels at 200 ppi corresponds to 12 by 8 inches, or 30.48 by 20.32 centimetres. These are mathematical dimensions, not a quality assessment of the image.
Choose a value for the intended use
Try several ppi values to compare sizes before making a layout. A small print viewed closely and a wall poster viewed from across a room have different practical needs. Inspect your source at a useful zoom level, consider any existing blur or compression, and make a test print. A higher number in the calculator cannot create missing detail or sharpen an out-of-focus photograph.
From calculation to paper
Check the actual pixel dimensions in your image editor or file information. Do not substitute the image's file size in bytes. The calculator does not resize the image, change metadata or account for printer margins. To place a picture across paper sheets, use the poster maker and check its displayed rendered resolution as well. Its PDF rendering limit is separate from the ppi value you explore here.
If the chosen dimensions need several sheets, make a tiled poster PDF and inspect its page count.
To keep those dimensions on paper, check actual-size PDF printing in your PDF viewer.
Work backwards from the paper
Switch to print size → pixels required to calculate the minimum whole-pixel dimensions for a chosen physical size and ppi. A4, Letter and A3 presets fill the paper dimensions. For A4 at 300 ppi, rounding upwards gives 2,481 × 3,508 pixels. This computes dimensions only; it does not upscale a file.
Pixels to cm or inches: one example
At 300 ppi, 1,200 pixels ÷ 300 = 4 inches. Multiply by 2.54 to get 10.16 cm. Conversely, 10 cm ÷ 2.54 × 300 = 1,181.10… pixels; this calculator rounds up to 1,182. Always supply PPI: pixels alone do not define a physical size.
A4 pixels and the rounding rule
A4 measures 21 × 29.7 cm. At 300 ppi, the exact dimensions are about 2,480.315 × 3,507.874 pixels. This tool rounds each side up, giving 2,481 × 3,508. Other tables round to the nearest integer and show 2,480 × 3,508. The one-pixel difference is a rounding convention, not extra image detail.
PPI does not change a file’s DPI metadata
PPI describes image pixels per printed inch; printer DPI describes dots of ink or toner. Entering 300 here only changes the calculation. It does not edit resolution metadata, resize a file or recover detail. The poster tool separately renders its PDF at 150 ppi.
References & further reading
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