How to Reduce Image File Size for Email and the Web
Whether you're fighting an attachment limit or a slow-loading page, the goal is the same: a smaller file that still looks good. This guide covers the real size limits you're up against and the fastest way to get under them.
Why your images are so big
Photos straight from a phone or camera are large for two reasons: high resolution (12 megapixels and up) and minimal in-camera compression to preserve editing latitude. A single photo can easily be 5–12 MB. That's wonderful for printing and terrible for email and web pages, where you almost never need that much data.
Email attachment limits
- Gmail: 25 MB per message (larger files switch to a Google Drive link).
- Outlook / Microsoft 365: 20–25 MB, though many corporate servers cap inbound mail at 10 MB.
- Practical advice: keep total attachments under 10 MB so they pass through every server in between.
For a handful of photos, compressing each to 300–800 KB keeps the whole email small and fast to download — with no visible quality loss for on-screen viewing.
Web page targets
Page speed is a ranking factor and a bounce-rate factor. Sensible targets:
- Hero / full-width images: 1600–2000px wide, 150–400 KB as WebP.
- In-content images: 800–1200px wide, 50–150 KB.
- Thumbnails: 300–600px wide, 10–40 KB.
The two-step method
Reducing file size is almost always a combination of resizing and compressing:
- 1. Resize the image down to the largest dimension it will actually be displayed at. This alone often cuts the file by 70%+.
- 2. Compress in WebP or JPEG at quality ~80. See compressing without losing quality for the details.
You can do both, for any number of images at once, with the free PixelTools compressor — set a maximum dimension, pick a format, and download a ZIP. Everything runs locally in your browser, so even sensitive photos never leave your device.
When you need an exact number
Some upload forms enforce a hard cap — "max 2 MB" or "under 500 KB." Rather than guessing at quality settings, use a target-size tool that automatically finds the best quality that fits:
Each one binary-searches the quality setting — and downscales if needed — to land just under your target while keeping the image as sharp as possible.