How to Reduce Photo File Size on Your Phone and Computer

Step by step

1. 1

   Understand what drives the file size

   A photo's size depends on three things: the pixel count, the JPG compression level, and the file format. Lowering the resolution makes the biggest difference, because going from 12 megapixels to about 2 megapixels can shrink the file several times over. For the web and online forms, you rarely need more than 1920 pixels on the longer side.

2. 2

   On your phone, use sharing options or an app

   On an iPhone, attach the photo to a message in the Mail app - when sending, the phone asks about the size, so pick Small or Medium. On Android, the options depend on the manufacturer, so the simplest route is installing a small free photo resizer app. Many messaging apps compress photos on send anyway. The iPhone saves photos in the HEIC format, which is lighter than JPG by itself, though some forms still require a regular JPG.

3. 3

   On Windows, use Paint or the Photos app

   In Paint, open the photo, click Resize, switch to Pixels, and enter a smaller value, for example 1920. Then choose Save As and the JPEG format. The Photos app has a similar Resize option in its three-dot menu, and it shows the approximate file size right away.

4. 4

   On a Mac, shrink the photo in Preview

   Open the photo in Preview, go to Tools → Adjust Size, and reduce the width in pixels. Then choose File → Export, pick the JPEG format, and move the quality slider. At a medium setting, the file is small and you won't see the difference on screen anyway.

5. 5

   Resize many photos at once

   On a Mac, select multiple photos in Preview and resize them all in one go. On Windows, add Microsoft's free PowerToys, which gives you a Resize pictures option when you right-click files. That saves a ton of time with dozens of photos.

6. 6

   Match the photo to a form's requirements

   Forms often have a hard limit on file size or dimensions, for example a photo under 1 MB or a specific pixel count. First reduce the resolution to what's required, and only then lower the JPG quality until you fit within the limit. Check the requirements in the form itself, because they can be very specific. ID-style photos are often described in millimeters and pixels at once, for example 35 by 45 mm at 300 dpi, so stick exactly to the stated numbers.

Resolution, file size, and compression - what actually changes the size

Resolution is the pixel count, for example 4000 by 3000. The more pixels, the bigger the file, and this is the lever with the biggest savings. Halving the longer side cuts the weight roughly fourfold, because pixels disappear in both dimensions at once. Always keep a copy of the original, because once a photo is downsized, you can't recover it later in full quality.

JPG compression works differently: the pixels stay, but the encoding becomes more lossy. A quality slider around 70-80 percent usually gives a file that's small and still looks good. Below 50 percent, visible artifacts appear around edges and lettering, so don't go that low without a reason.

JPG or PNG - and when to use which

For photos, pick JPG, because it compresses photographs far more aggressively and the file weighs megabytes instead of tens of megabytes. PNG keeps every pixel without loss, so the files are large, but it's excellent for screenshots, logos, and graphics with text, where sharp edges have to stay sharp.

If you save a camera photo as a PNG, you get a huge file with zero benefit. The other way around, a heavily compressed JPG will blur the fine text on a screenshot. Match the format to the content, and the size will come out sensible on its own.

Frequently asked questions