Few things are as disappointing as a photo that looks great on a phone and turns out soft and blocky on paper. The cause is almost always the same: the picture did not have enough pixels for the size it was printed at. The good news is that checking this in advance takes less than a minute, and it only needs one small calculation.
The rule of thumb
For a sharp print, aim for about 300 pixels for every inch of paper. This figure is the printing industry’s standard for pictures viewed at arm’s length. Multiply the print width and height in inches by 300, and you have the pixel size you need. Pictures that are viewed from further away, like posters and banners, can get away with much less.
Common sizes and the pixels they need
- 4 x 6 inch (10 x 15 cm): 1200 x 1800 pixels.
- 5 x 7 inch: 1500 x 2100 pixels.
- 8 x 10 inch: 2400 x 3000 pixels.
- A4 (8.3 x 11.7 inch): about 2480 x 3508 pixels.
- A3 (11.7 x 16.5 inch): about 3508 x 4961 pixels.
- Passport photo, 35 x 45 mm: about 413 x 531 pixels.
What your phone gives you
A typical modern phone photo is around 4000 x 3000 pixels, or twelve megapixels. At 300 pixels per inch, that prints about 13 x 10 inches, which is larger than A4. In other words, a recent phone photo is plenty for most prints, as long as you use the original file and not a copy shrunk by a messaging app.
Checking your file
Right-click the picture on a computer, open Properties and look at the Details tab for the width and height in pixels. On a phone, open the photo info in your gallery. Divide the pixel width by 300 to see the largest sharp print size in inches. For example, 2400 pixels wide gives you 8 inches at full quality.
What if you are short of pixels?
You have a few honest options. Print smaller, since a photo with 1200 pixels is great at 4 x 6 inches and poor at 8 x 10. Accept 200 pixels per inch for larger prints that will not be examined closely, which is usually acceptable for wall pictures. Retake the photo at the highest camera setting. Or use enlargement software, understanding that it only smooths the result and does not add true detail.
Cropping changes the maths
Cropping throws pixels away. If you take a 4000 x 3000 picture and crop it to a small part of the scene, you might end up with only 1500 pixels across, which is enough for a 5-inch print and no more. Decide the print size before you crop heavily, and watch the pixel numbers after cropping. The Image Cropper keeps the original resolution of the pixels you keep, so nothing extra is lost.
Aspect ratio and paper shape
Photo paper has its own shape. A 3:2 camera photo fits 4 x 6 inch paper exactly, but it does not fit 8 x 10 inch paper, which is 5:4. If you print without cropping first, the printer will either cut off the edges or leave white bars. Choose a ratio that matches your paper before you send the file to print. The guide on cropping to the right shape covers the common ratios.
Viewing distance changes everything
A large banner seen from five metres away does not need 300 pixels per inch. Your eyes cannot resolve that detail at that distance. Billboards often use only a few dozen pixels per inch. The rule is simple: the further the viewer stands, the fewer pixels you need. For anything held in the hand, like a photo, card or flyer, stay close to 300.
An example with a notice board
Suppose a group photo looks poor when printed for a school notice board. The picture arrived through a chat app and measures only 960 pixels across. Printed at A4 width, that is about 115 pixels per inch, well below the 300 target, so the faces look soft. Asking the photographer for the original file, which is likely over 4000 pixels wide, solves the problem completely. If a print matters, always ask for the original.
File format for printing
Send the original JPG at high quality, or a PNG if the design includes sharp text. Avoid sending a heavily compressed copy, since compression artefacts become more visible when enlarged on paper. If the print shop has its own instructions, follow those first, since they know their printers.
A quick checklist
- Decide the print size and paper shape.
- Multiply inches by 300 to find the pixels you need.
- Check the pixels in your file.
- Crop to the paper shape before sending.
- Send the original, not a shared copy.
With that calculation in your pocket, you will know before you pay whether a print will be sharp, and you will avoid the unpleasant surprise of a blurry picture on the wall.