How do I make a file or photo smaller?

Reducing photo, PDF and document sizes without losing the quality that matters for the purpose.

Difficulty: beginner
Time: 15 min
Read: 2 min

Short answer

For photos, reduce the dimensions rather than only the quality — a photo for email does not need to be 6000 pixels wide. For PDFs, most systems have a 'reduce file size' export option built in.

File size is usually driven by dimensions and embedded images rather than by anything mysterious. Reducing what the file does not need for its purpose is more effective and less destructive than compressing everything harder.

What you'll need

The file
Built-in photo or PDF tools (optional)

Step by step

Work out what size it actually needs to be.Email attachments usually have a 25MB limit. A photo for on-screen viewing needs perhaps 1500 pixels wide; for printing, considerably more.
Reduce photo dimensions first.Halving the width and height quarters the file size with no visible loss on screen. This is far more effective than quality compression alone.
Then reduce quality if still needed.JPEG quality around 80% is visually near-identical to 100% at a fraction of the size. Below about 60% artefacts become visible.
Use the built-in export options.Preview on Mac, Photos on Windows, and phone share sheets all offer size options. No third-party tool is needed for most cases.
For PDFs, use the reduce-size export.Preview on Mac has a Quartz filter for it; many PDF tools have 'optimise' or 'reduce file size'. It mainly downsamples embedded images.
Remove what the file does not need.Unused pages, high-resolution embedded images in documents, and embedded fonts all add size unnecessarily.
Zip multiple files together.It bundles them into one and compresses text-based files well. Photos and video are already compressed and shrink very little.
Consider sharing a link instead.For anything genuinely large, especially video, a cloud link is simpler than fighting the file size.

Tips

Keep the original. Compression is lossy and irreversible — always work on a copy for the smaller version.
HEIC and WebP formats produce much smaller files than JPEG at the same quality, but check the recipient can open them.
Screenshots as PNG are often much larger than needed. Saving as JPEG reduces them substantially for photographic content.

Common mistakes

Compressing quality without reducing dimensions — Dimensions drive most of the size. A 6000-pixel photo compressed hard still looks worse and is still large.
Overwriting the original — Compression is irreversible. Once the quality is gone, it cannot be recovered.
Zipping photos or video expecting a big saving — They are already compressed formats. Zipping them gains very little.

Questions people ask

How do I make a photo smaller for email?

Reduce its dimensions — around 1500 pixels wide is plenty for on-screen viewing — then export at about 80% JPEG quality. That typically reduces the file by 90% or more.

How do I reduce a PDF file size?

Use the built-in reduce-size or optimise export in your PDF viewer. It mainly downsamples the embedded images, which are usually what makes a PDF large.