How to calculate image dimensions
- Enter the original width and height in pixels.
- Choose how to scale: by percentage, to a new width or to a new height.
- Set a DPI to see the equivalent size in centimetres and inches.
- Use the results in Resize Image to change the actual file.
Scaling without distortion
To keep proportions, both sides must change by the same factor. New height equals new width multiplied by the original height divided by the original width. A 4000 × 3000 photo resized to 1200 pixels wide becomes 1200 × 900. The calculator rounds to whole pixels, since images cannot contain fractions of a pixel. Percentage scaling works the same way: 50% of 4000 × 3000 is 2000 × 1500.
Use the image dimension calculator before resizing or printing to see the exact pixel or centimetre dimensions you will get.
Converting pixels to print sizes
Physical size in inches is pixels divided by DPI, and centimetres are inches multiplied by 2.54. At 300 DPI an A4 page (21 × 29.7 cm) needs 2480 × 3508 pixels, and a 4 × 6 inch print needs 1200 × 1800 pixels. Working backwards is just as useful: a form asking for a 3.5 × 4.5 cm photo at 300 DPI needs about 413 × 531 pixels.
Typical uses
Use the calculator to prepare files for print shops, to meet application forms that specify sizes in centimetres, or to plan web image sizes before exporting. To check an existing file, the Image Resolution Checker reads its dimensions for you, and the Aspect Ratio Calculator helps with ratios such as 16:9.
Frequently asked questions
What DPI should I use for printing?
300 DPI is standard for photos and documents viewed up close; 150 DPI is fine for posters viewed from a distance.
Does changing DPI change the image?
No. DPI only states how large to print the pixels. Only resizing changes the pixel dimensions.
How do I convert cm to pixels?
Divide the centimetres by 2.54 and multiply by the DPI. For example, 5 cm at 300 DPI is about 591 pixels.
Do I need to upload an image?
No. Just type the numbers; nothing is uploaded.