Will this photo print well? A ten-second check before you order a print

A photo that looks sharp on a phone can fall apart at 60 centimetres wide. The screen is small, bright and forgiving. Paper is none of those things. Before you commit a favourite image to a wall, check three things.

1. How many pixels do you actually have?

Open the photo's details. You are looking for two numbers, like 4000 × 3000. That is the raw material. Printers like around 300 pixels per inch for close viewing and are perfectly happy with 150 at wall distance. The arithmetic:

A typical 12-megapixel phone shot (4000 pixels on the long edge) prints beautifully at A3 and holds up at A2 on a wall. A1 wants a real camera, or a phone in its highest-resolution mode, or a subject that forgives softness.

2. Zoom to 100 percent and look at the shadows

Noise hides in the dark parts. Pinch in on the tyre, the underside of the bumper, the interior behind the glass. Coloured speckle there, or a smeary, painted look where the phone's software tried to hide the speckle, will show on paper as a mottled grey. Photos taken in good light almost never have this problem; night shots and shaded shots often do.

3. Check the crop against the size

Print sizes have fixed proportions. A2 and A3 are roughly 1.41 to 1. Fifty by seventy is 1.4 to 1. Thirty by forty is 1.33 to 1. A phone shoots 4 to 3, a camera 3 to 2, a cinematic crop closer to 2 to 1. Something has to give at the edges. Ask yourself: if the top and bottom lose a strip, is the car still whole? If the answer is no, choose the size that matches the shape, or reshoot with more room around the car.

What doesn't matter as much as people think

• Megapixels beyond what the table needs. Extra pixels don't rescue a photo taken in bad light.
• Filters. A heavy filter on screen becomes a heavy filter on paper, only bigger. Print from the cleanest version you have.
• Sharpening. Printers and print labs add their own. Over-sharpened files get crunchy halos along the body line.

Three checks, ten seconds. If the numbers work and the shadows are clean, the print will look like the screen, only better, because paper doesn't glow.