What Is DPI? How to Convert cm and Inches to Pixels (Print Size Guide)

Short answer: DPI tells you how many image pixels are printed per inch of paper. To convert a print size to pixels, divide centimetres by 2.54 and multiply by the DPI, which gives 10 cm = 1181 px at 300 DPI. For a sharp print you want about 300 DPI for things held in the hand and roughly 100–150 DPI for posters. Imgovo’s DPI & Size Calculator converts cm, mm and inches to pixels and back, and checks whether your photo has enough pixels for a given print size.

What does DPI mean?

An image is a grid of pixels, for example 3000 × 2000. A print has a size on paper, for example 10 × 15 cm. DPI links the two. It says how many of the image’s pixels are laid down on each inch of paper.

The relationship is simple:

• pixels = inches × DPI
• inches = pixels ÷ DPI
• 1 inch = 2.54 cm = 25.4 mm

So the same photo can be printed small and sharp or large and soft. A photo that is 3000 px wide prints 10 inches wide at 300 DPI. Printed 30 inches wide, it has only 100 DPI and will look soft from close up.

DPI or PPI?

Strictly speaking, PPI (pixels per inch) belongs to images and screens, and DPI (dots per inch) belongs to printers, which lay down tiny dots of ink. In practice almost every program and print shop says DPI when it means PPI. The DPI & Size Calculator treats both as the same number, so you can use either word.

How to convert cm, mm or inches to pixels

1. Convert the length to inches. Divide centimetres by 2.54, or millimetres by 25.4.
2. Multiply the result by the DPI you want.
3. Round to a whole pixel.

Example: how many pixels is 10 cm at 300 DPI? 10 ÷ 2.54 = 3.937 inches. 3.937 × 300 = 1181 pixels.

To go the other way, divide pixels by the DPI to get inches, then multiply by 2.54 for centimetres.

You can skip the arithmetic with the DPI & Size Calculator. Type into any box (px, cm, mm or inch) and the others update. If you change the DPI, the side you did not type in last is recalculated. There are quick buttons for 72, 96, 150, 300 and 600 DPI, a lock for the aspect ratio and a button that swaps width and height.

Pixels needed for common print sizes

These are the pixel counts you need for a sharp print. The calculator shows the same table for 300 and 150 DPI.

Photo prints

Print size	At 300 DPI	At 150 DPI
9 × 13 cm	1063 × 1535 px	531 × 768 px
10 × 15 cm	1181 × 1772 px	591 × 886 px
4 × 6 in	1200 × 1800 px	600 × 900 px
5 × 7 in	1500 × 2100 px	750 × 1050 px
13 × 18 cm	1535 × 2126 px	768 × 1063 px
15 × 20 cm	1772 × 2362 px	886 × 1181 px
8 × 10 in	2400 × 3000 px	1200 × 1500 px
20 × 30 cm	2362 × 3543 px	1181 × 1772 px
30 × 40 cm	3543 × 4724 px	1772 × 2362 px
40 × 60 cm	4724 × 7087 px	2362 × 3543 px

Paper sizes

Paper	Size	At 300 DPI	At 150 DPI
A6	105 × 148 mm	1240 × 1748 px	620 × 874 px
A5	148 × 210 mm	1748 × 2480 px	874 × 1240 px
A4	210 × 297 mm	2480 × 3508 px	1240 × 1754 px
A3	297 × 420 mm	3508 × 4961 px	1754 × 2480 px
A2	420 × 594 mm	4961 × 7016 px	2480 × 3508 px
US Letter	8.5 × 11 in	2550 × 3300 px	1275 × 1650 px
US Legal	8.5 × 14 in	2550 × 4200 px	1275 × 2100 px

ID photos and cards

Item	Size	At 300 DPI
Passport photo (EU)	35 × 45 mm	413 × 531 px
Passport photo (US)	2 × 2 in	600 × 600 px
Business card (EU)	85 × 55 mm	1004 × 650 px
Business card (US)	3.5 × 2 in	1050 × 600 px

Passport and ID photo rules differ by country, so check the requirements of the authority before you print. The calculator provides the pixel size; the rules for background, head size and format come from the authority.

Large prints: how many pixels for 70 × 100 cm?

Posters are viewed from further away, so they need fewer pixels per inch. For a 70 × 100 cm print:

DPI	Pixels needed
300 DPI	8268 × 11811 px (about 97.7 megapixels)
150 DPI	4134 × 5906 px
100 DPI	2756 × 3937 px

Hardly any camera produces 300 DPI at that size, and nobody expects it. At 100–150 DPI the print looks fine from the distance at which you look at a poster. As a rule of thumb, the further away the viewer stands, the lower the DPI you can accept.

Which DPI do I need?

Use	DPI to aim for
Photos, flyers, business cards, brochures (held in the hand)	About 300
Posters and wall prints (seen from a distance)	About 100–150, up to 200 for closer viewing
Large banners and billboards	Lower still, because the viewer stands far away
Screens, websites, social media	Not relevant, only pixel dimensions matter

If you are preparing an image for a website or a social platform, think in pixels and not in DPI. See How to resize an image without losing quality and the social media image sizes cheat sheet.

How to check whether your photo is big enough to print

You need two numbers: the pixel size of the photo and the print size you want. The calculator can read the pixel size for you.

1. Open the DPI & Size Calculator.
2. In “Check my image for printing”, drop your photo into the box, click to choose it, or paste it from the clipboard. JPG, PNG, WebP, HEIC and TIFF files work. You can also type the width and height in pixels.
3. Read the results table. It lists the print sizes, the DPI your photo reaches at each size, a print quality column and a note.
4. Pick a size where the DPI is high enough for how the print will be used.

Example: a 12-megapixel phone photo of 4000 × 3000 px prints at 33.9 × 25.4 cm at 300 DPI, or at 67.7 × 50.8 cm at 150 DPI. That is more than enough for A4 and still good for a poster up to about A2.

A second example from the calculator page: a photo of 3000 × 2000 px prints at 25.4 × 16.9 cm at 300 DPI, or 50.8 × 33.9 cm at 150 DPI.

If you want to see the pixel size of any file yourself: on Windows, right-click the file, choose Properties and open the Details tab. On a Mac, open the file in Preview and choose Tools, then Show Inspector.

When the shape of the photo and the paper differ, a print is cropped to fill the paper. Keep important parts away from the edges, or crop the photo to the paper’s shape first with Crop Image.

Saving a file with a DPI label

Some print services or forms ask for “a file at 300 DPI”. The calculator can save a copy with that label:

• Download with DPI saves the file with the DPI you chose.
• For JPG and PNG files, only the DPI label is replaced. The picture is not re-encoded and not resampled.
• Other formats are re-saved as JPG (95% quality) or PNG (lossless).
• You can also choose Re-save as JPG (95% quality) or Re-save as PNG (lossless).

The label does not add detail. If a photo has too few pixels for the print size, writing 300 into the file does not fix it.

What the calculator does not do

• It does not resample the picture. Changing the DPI never changes the number of pixels.
• It does not define quality categories. The “Print quality” column compares your photo with the print size; the rule of thumb is 300 DPI or more for sharp results in the hand and 150–200 DPI for posters seen from a distance.
• It does not know your printer’s requirements. Ask the print shop if you are unsure.

If the image is too small for the print

1. Print smaller. Use the results table to find the largest size that reaches your DPI target.
2. Find the original. A photo that was shared through a messenger or social network has often been shrunk and compressed. The original file may have far more pixels.
3. Accept a lower DPI for prints viewed from a distance.
4. Enlarge the pixels. Resize Image can increase the pixel size, which can satisfy a minimum size on a form. It makes the file bigger but cannot add real detail, so the print stays soft.

Common mistakes

• Believing 72 DPI is for the web and 300 DPI is for print. Online, DPI is ignored. A 1200 px image is 1200 px, whatever its label says.
• Raising the DPI to “improve” a photo. It only changes the print size the file claims.
• Forgetting the viewing distance. A poster at 300 DPI wastes pixels no one can see.
• Mixing up pixels and centimetres. Always convert through inches, or let the calculator do it.

Do it now

Open the DPI & Size Calculator, enter your size or drop in a photo, and see at once which prints it supports. Everything runs in your browser, and nothing is uploaded.