Prepare a poster, canvas or photo-book page from an order specified in centimeters. Convert the finished dimensions to pixels at the requested PPI before building the artwork.
Start from the centimeter order
- Enter the ordered width and height in centimeters, or choose A4, A3, A2 or a photo-size preset.
- Set the requested PPI; keep any margins, wrap or bleed distinct from the finished size.
- Review exact and rounded pixels, then copy the target or open Image Resizer.
Convert centimeters to inches before multiplying
An inch is exactly 2.54 centimeters. Divide the centimeter edge by 2.54, then multiply by PPI: px = cm ÷ 2.54 × PPI. A 20 cm edge at 300 PPI needs about 2362.205 pixels, rounded to 2362 by this calculator.
For a 20 × 25 cm photo-book image at 300 PPI, the rounded target is 2362 × 2953 pixels. Check whether the book designer’s slot includes a trim allowance. A full page, a picture box and a two-page spread are different production targets.
Metric canvas examples at 300 PPI
These values use nearest whole-pixel rounding. If a supplier requires at least 300 PPI at the exact physical size, use the unrounded numbers to check whether an edge should be rounded upward instead.
| Canvas | Centimeters | Rounded pixels at 300 PPI |
|---|---|---|
| A4 | 21 × 29.7 | 2480 × 3508 |
| A3 | 29.7 × 42 | 3508 × 4961 |
| A2 | 42 × 59.4 | 4961 × 7016 |
| Photo book image | 20 × 25 | 2362 × 2953 |
Keep page geometry and source detail separate
Calculate the required grid before drawing or exporting. When placing an existing photograph, check its retained crop against the target grid. Resampling a small source can fill the dimensions but cannot recover detail that was not recorded.
Canvas wrap, binding gutters and safe areas are supplied by the printer, not inferred from PPI. Save those requirements with the job so a later revision does not accidentally use the visible area as the full production canvas.
Image pixels and CSS pixels
CSS defines 96 CSS pixels per CSS inch for layout. That relationship is not the physical density of every screen, nor a required density for a printed image. Here, PPI is your explicit print assumption; browser zoom does not change the file’s stored pixels.
Frequently asked questions
Why is an A4 pixel edge not an exact integer?
21 cm divided by 2.54 centimeters per inch, multiplied by 300, is fractional. Raster images need whole pixels, so the calculator shows the rounding.
Do I calculate a photo-book spread as one page or two?
Use the dimensions from the book template, including any gutter or trim allowance. Two visible pages do not always equal the supplier’s complete spread canvas.
Can I use the same pixel grid for a larger canvas print?
The grid will provide fewer pixels per inch at a larger physical placement. Recheck density and the required wrap area before ordering.