Megapixel Calculator

Megapixels are the headline number on every camera and phone, but the figure that actually matters is what those pixels let you do, and this calculator turns a resolution into the answers you need. Enter the width and height of an image in pixels and it returns the total megapixels, the aspect ratio in its simplest whole-number form, and the largest size you can print at high quality, shown in both inches and centimetres. A megapixel is simply one million pixels, so the calculation multiplies the width by the height and divides by a million, but the related figures are where it becomes genuinely useful. The aspect ratio tells you the shape of the image, whether it is a classic 3 by 2 photo, a 16 by 9 widescreen frame or a square, which matters when you crop, frame or fit an image to a screen or print. The print size is worked out at 300 dots per inch, the standard for sharp photographic prints, by dividing each pixel dimension by 300, so you can see at a glance whether a photo has the resolution to print at A4, A3 or larger before it starts to look soft. That helps you decide whether an image is big enough for a poster, how much you can crop and still print well, or whether you need to shoot at a higher resolution. It is handy for photographers, designers, print buyers and anyone choosing a camera or preparing images for print or screen. More megapixels are not automatically better, since lens, sensor and light matter too, but knowing the numbers helps you make the right call. The formulas and a worked example are below.

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