Resize an image in cm when the size comes from a lab order, a frame or a template: they state centimetres, and a file only has pixels. This page converts at 300 DPI, opens the editor on 10 × 15 cm, and saves exactly the pixels that print needs. Part of the image resizer.
Resize image in cm: centimetres to pixels at 300 DPI
1 cm at 300 DPI
118 px (118.11 unrounded)computed
10 × 15 cm
1181 × 1772 px, the size this page opens oncomputed, sides rounded
A4, 21 × 29.7 cm
2480 × 3508 pxcomputed, sides rounded
The formula
pixels = cm ÷ 2.54 × DPIWikipedia, Pixel density
A DPI tag in a file
metadata only: it changes no pixelWikipedia, Dots per inch
Output format
– / –
Drop images or browse
JPEG · PNG · WEBP · AVIF · HEIC · up to 50 at once · max 30 MB each
HEIC
PNG
JPEG
AVIF
WEBP
Advanced settings1 on
SmallerAutoBetter
Auto tunes each image.
A hard cap for the number your form demands.
KB
A floor for forms that refuse small files.
Max resolution
×
Empty side keeps the ratio. Never enlarges.
Presets
Every named size, one editor
The same editor, the size already pressed. Pick the document or the platform.
Source: photo.jpg, 576.8 KB at 1920×1280, through the preset this page opens on (the centre cropped to the ratio and scaled to the size), then the engine at its defaults. The row is the real output.
Every byte count is the size of the actual file our engine produced from the named source, the same bytes you would download, not an estimate. The reference photo is one of our own photographs, an iguana on a branch, and the camera photo is a real one too. Drop your own file into the tool above to rerun any of them. How we measure names the sources and the settings.
Answered
How many pixels is a centimetre, and why does this page assume 300 DPI?
118 pixels, at 300 DPI, and the second half of that sentence is the whole point.
A pixel has no size of its own. It gets one only when a printer, a screen or a scanner lays it down at a density, so many pixels to the inch. The arithmetic is short: pixels equal centimetres divided by 2.54, times the DPI, because the inch is defined as 25.4 mm exactly. At 300 DPI a centimetre is 118.11 pixels, rounded to 118 when a whole one is needed.
300 is the print convention, not a law: about the point beyond which the unaided eye stops seeing extra detail at reading distance, and the resolution the spec card above converts at. A photo lab, a frame shop or a certificate template that writes centimetres means 300 unless it says another number. When it says 150 or 600, that number wins, and the arithmetic changes with it. One more thing worth saying out loud: a DPI value stored inside a file is metadata. It tells a program the intended print size and moves no pixel, so a portal that checks dimensions reads the pixels and ignores it.
Computed
How many pixels are 9 × 13, 10 × 15, 13 × 18, 15 × 20, 20 × 30 cm and A4 at 300 DPI?
The lab sizes, computed on this page by the same arithmetic the editor runs, each side rounded to a whole pixel on its own.
The third column shows what was rounded: a centimetre never lands on a whole pixel, and the difference is under half a pixel either way. Type any of them into the Custom size box in cm and the line under the fields prints the same number.
Size
Pixels at 300 DPI
Before rounding
Ratio
9 × 13 cm
1063 × 1535
1062.99 × 1535.43
9:13
10 × 15 cm
1181 × 1772
1181.10 × 1771.65
2:3
13 × 18 cm
1535 × 2126
1535.43 × 2125.98
13:18
15 × 20 cm
1772 × 2362
1771.65 × 2362.20
3:4
20 × 30 cm
2362 × 3543
2362.20 × 3543.31
2:3
A4, 21 × 29.7 cm
2480 × 3508
2480.31 × 3507.87
1:1.41
Computed at render time from pixels = cm ÷ 2.54 × 300, each side rounded to the nearest whole pixel. The inch is 25.4 mm by definition, so nothing here is approximate except the rounding.
Answered
How do I resize an image in centimetres with the editor?
On the Crop tab the Custom size box opens in centimetres, its two fields reading the size in force, 10 × 15 on arrival, with the 10×15 cm tile lit in the ID & print group above them.
The unit menu under the fields switches to px, mm or in when a form states those. The link icon between the fields keeps the shape while you type, so for a size with a different shape tap it once to unlink, then type the width and the height. As you type, the line under the fields prints what they become: type 13 and 18 and it reads 1535 × 2126 px at 300 DPI. Press Apply and the crop frame snaps to that shape. The size is now the export size, whatever part of the picture you choose.
Answered
What happens to my photo when its shape is not the print's shape?
Something has to give, and the Crop / Fit switch under the size tiles decides what.
Our reference photo is 3:2, held wide; 10 × 15 cm is 2:3, a tall frame. Crop cuts the picture to the print’s shape: a tall 10 × 15 frame inside our wide photo keeps 44 percent of the width, and you drag the frame to choose which part. Fit keeps the whole picture inside the size and fills the rest with a colour, white, black, grey, green or one you pick from the well, so the print carries a plain band instead of losing an edge. The export is exactly the size either way. What the editor never does is stretch: a face pulled to fit a frame is the one result nobody ordered.
Measured
Does my photo have enough pixels for a 10 × 15 cm print?
Divide its pixels by 118 and you have its size in centimetres at 300 DPI.
Our 1920 × 1280 reference photo prints 10.8 cm tall at that density, short of 15. Its 2:3 crop is 853 × 1280. The preset still exports 1181 × 1772, because an exact size is a promise, so the engine enlarged the crop 1.4 times and saved it at 232.3 KB. Enlargement adds pixels, not detail. A camera or phone photo has the pixels to spare: the 9.8 MB camera photo the home page uses is 4964 × 2782, which covers 42 × 23.6 cm at 300 DPI. When yours falls short, order the smaller print, or accept a lower density and tell the lab.
Source
Output
Pixels
Result
What changed
Reference photo
10 × 15 cm
1181×1772
232.3 KB
crop enlarged 1.4×, no more detail
4.1 MB PNG
full size, as JPEG
1920×1280
273.9 KB
the format change alone
4.1 MB PNG
400 px wide, as JPEG
400×267
18.3 KB
93% under the row above: 4% of the pixels
Sources: photo.jpg, our reference photo, 576.8 KB at 1920×1280, through this page's preset (the centre cropped to 2:3 and scaled to 1181 × 1772), and photo.png, the 4.1 MB PNG of the same photo, saved as JPEG at Auto at full size and at 400 px wide. Each row is the file the engine produced.
Answered
Will resizing in cm make the file smaller?
Only when the pixel count drops, and then steeply.
The last two rows of the table are one JPEG at two sizes: 273.9 KB at full size, 18.3 KB at 400 pixels wide, 93 percent less for 4 percent of the pixels. At 21 percent of each side the photo keeps 4 percent of its pixels, and no quality setting can match that. A print size usually goes the other way. 1181 × 1772 is more pixels than most screen images carry, so the file grows with them. When a portal checks the bytes as well as the centimetres, set Max file size in Advanced settings before you save; the export lands at the size and under the cap in one pass, and the cap never overshoots.
Be sure first
When centimetres are the wrong unit
The print shop wants 150 or 600 DPI?
The box converts at 300 only. Multiply centimetres by their DPI, divide by 2.54, and type the pixels with the unit on px.
The form states pixels?
Type pixels. A form that says 600 × 600 wants exactly that, and any centimetre figure beside it is a hint, not the rule.
A screen, a slide, a wallpaper?
Screens have no unit but the pixel. The 1920 × 1080 page opens on the Full HD frame with no DPI in sight.
A named document size?
The passport pages carry each frame with its official rules and the portals that state them. This page carries the arithmetic.
A whole folder to one bound?
The resize tool bounds 50 images at once by Max resolution, never enlarges, and returns one ZIP.
The size is already pressed above. One drop settles most of these.
Q:How do I resize a photo in centimetres?
Drop the photo into the tool. The editor opens on the Crop tab with 10 × 15 cm already in force, which is 1181 × 1772 pixels at 300 DPI. For another size, the Custom size box is already in centimetres: unlink the sides if the shape differs, type the width and height, and press Apply. Drag the frame over the part you want, or press Fit to keep all of it, then Save.
Q:How many pixels is 10 × 15 cm at 300 DPI?
1181 × 1772 pixels. The arithmetic is centimetres divided by 2.54, times 300: 10 cm is 1181.10 pixels and 15 cm is 1771.65, each rounded to a whole pixel. The inch is fixed at 25.4 mm, so the conversion is exact and only the rounding is an approximation. The editor exports that size to the pixel when you save.
Q:Why does DPI matter when resizing in cm?
Because a pixel has no size of its own. It only gets one when something prints or displays it at a density, so many pixels to the inch. The same 1181 × 1772 pixels are 10 × 15 cm at 300 DPI and twice that at 150. A centimetre figure is meaningless without the DPI beside it, which is why the number always travels with its DPI.
Q:What DPI should I use for printing?
300 DPI, unless the print shop says otherwise. It is the print convention, close to the point past which the eye stops seeing extra detail at reading distance. If your lab asks for 150 or 600, its number wins: multiply centimetres by their DPI and divide by 2.54, then type the pixels into the Custom size box.
Q:Which unit should I use to change the dimensions of an image, cm or pixels?
Use the unit the order is written in. A lab, a frame or a certificate template states centimetres, so type centimetres and let the box convert. A web form, a portal or a screen states pixels, so type pixels. Both end in the same place, an export sized in whole pixels; the unit only decides who does the arithmetic, you or the editor.
Q:Will image quality suffer when I resize in cm?
Not when the photo has at least as many pixels as the print needs. Scaling down keeps detail; the file is re-encoded once at high quality. Quality suffers when the photo is smaller than the size, because an exact-size preset enlarges it and enlargement invents nothing. Our 1920 × 1280 reference photo's 853 × 1280 crop is enlarged 1.4 times to reach 10 × 15 cm, and gains no detail doing it.
Q:Does the photo resizer in cm also take mm and inches?
Yes. The unit menu under the Custom size fields offers px, mm, cm and in, and all three physical units convert at 300 DPI. A size in millimetres is the same size divided by ten; an inch is 25.4 mm exactly. The millimetre page opens on 50 × 50 mm and the inch page on 4 × 6 in, each with its own table and its own examples.
Q:Will resizing in cm reduce the file size?
Only if the pixel count goes down. Our reference photo saved as a full-size JPEG is 273.9 KB; at 400 pixels wide it is 18.3 KB, 93 percent less for 4 percent of the pixels. A print size sets the pixels: 10 × 15 cm is 85 percent of our photo's pixels, and came back at 232.3 KB.
Q:Can I resize several images in cm at once?
One photo at a time in the editor, because a centimetre size has a shape and the crop that meets it needs your eye. Each save lands in the same download list, so a set is drop, place, save, next. For many files to one pixel bound with no crop, the resize tool takes 50 at once and returns one ZIP.
Q:Does the saved file remember its size in cm?
It remembers its pixels, which is what matters. A DPI value in a file is metadata: it tells a program the intended print size and changes no pixel. A portal that checks dimensions reads the pixels and ignores the tag, and a lab prints the pixels at the size you order. We make no promise about a DPI tag in the export; the 1181 × 1772 pixels are the promise.
Q:How do I resize in cm without cropping the photo?
Press Fit instead of Crop once the size is in force. Fit scales the whole picture to sit inside the centimetre size and fills the rest with a colour: white, black, grey, green or one you pick. The export is still exactly the size, so a lab prints it with a plain border instead of cutting a strip off the picture.
Q:Do you keep my photo after I resize it?
No. We keep nothing: files are processed and wiped automatically, never archived and never used for anything else. Saving strips EXIF metadata, including GPS location, by default, so a photo you hand to a lab or a portal carries no record of where it was taken. No account, no watermark, and the resize is free.
