Why are my photos so large?

You take one photo, attach it to an email, and the message is suddenly 4 MB. Nothing about the picture looks four megabytes worth of complicated. The explanation is simple arithmetic: file size is driven by how many pixels the camera recorded, not by how interesting the subject is.

Megapixels are just multiplication

A camera advertised as 12 megapixels produces images about 4032 pixels wide and 3024 pixels tall. Multiply those and you get a little over 12 million pixels — twelve megapixels. Every one of those pixels has to be stored with a colour value.

Now compare that with the screen you are reading this on. A typical laptop displays about 2 million pixels; a phone about 2 to 3 million. So a single 12 megapixel photo carries roughly four to six times more detail than the entire screen it will be shown on. The rest is stored, uploaded, downloaded and decoded for nobody.

The four things that decide the file size

• Pixel count — the dominant factor. Double the width and height and you have four times the pixels to encode.
• Format — a JPEG stores a photo in far fewer bytes than a PNG of identical dimensions, because PNG is lossless and records every pixel exactly.
• Quality setting — JPEG and WebP let the encoder throw away detail the eye is unlikely to notice. Dropping from 95 to 75 typically halves the file with no visible change at normal viewing sizes.
• Content — fine texture costs more than flat areas. A photo of gravel is heavier than a photo of a wall, at the same dimensions and settings.

Why screenshots are so much bigger than they look

A screenshot is usually saved as PNG, which is lossless. That is the right choice for text and interface graphics, because lossy compression smears the edges of letters. The price is that a full-screen screenshot of a detailed page can easily be 2–5 MB, and one of a spreadsheet larger still. If the screenshot is a photograph of a document rather than crisp UI, saving it as JPEG or WebP instead can cut it by 80% or more with no meaningful loss.

Modern phone formats are not always the culprit

iPhones and many Android phones capture in HEIC, which is smaller than JPEG for the same quality, and then convert to JPEG when you share the file with other apps. That conversion is why an image that looked small in your gallery arrives at 5 MB. Nothing is broken; you are simply receiving the full-resolution original.

Phones with a 48 or 50 megapixel sensor add another wrinkle: many only use the full resolution in a special mode or in good light, and otherwise combine pixels into a 12 megapixel result with better low-light performance. Check the actual dimensions of the file — the number on the camera spec sheet is not always the number in the file.

What actually shrinks a photo

1. Resize it. Decide the largest size it will be displayed at — 1280 pixels wide for a blog image, 1920 for a full-width banner — and reduce it to that. This is where most of the saving comes from. Use the image resizer.
2. Compress it. Re-encode at a sensible quality: 70–80 for photos, lower for thumbnails. Use the compressor.
3. Pick the right format. WebP for the web, JPEG for maximum compatibility, PNG only when you need transparency or lossless flat colour.
4. Check the result at 100%. If you cannot see a difference on screen, there is no difference that matters.

If a form or a portal demands an exact limit — "under 500 KB", "maximum 200 KB" — skip the guesswork and use the target size tool, which finds the highest quality that still fits.

When you should keep the big file

Compression is for delivery, not for archiving. Keep the originals on a drive or in cloud storage. You will want the full-resolution version for printing, for a future website redesign that uses larger images, or for the day a better format arrives and you want to re-export. Deleting the original to save space is a decision you cannot undo.

Frequently asked questions