Reduce Image Size for Email: Dimensions, Quality and Format

To reduce image size for email, resize the photo first and compress it second. A phone photo at 4032 × 3024 pixels is usually 3 to 5 MB. Scale it to 1600 pixels on the long edge, save it as JPEG at quality 75 to 80, and it typically lands between 200 and 400 KB while still looking sharp on any screen. For images inside a newsletter, go smaller still: 1200 pixels wide is enough for a 600-pixel email template on a high-density screen. Format matters less than people think, with one exception: WebP still isn't safe in email.

Why dimensions come before quality

File size grows with the number of pixels. A 4032 × 3024 photo has about 12.2 million of them. At 1600 × 1200 it has 1.9 million, roughly a sixth. That cut alone takes most photos from several megabytes to well under one, before you touch the quality slider at all.

Compressing a full-size photo instead works, but you have to push quality much lower to reach the same file size, and that's when you start seeing blocky skies and smeared faces. Resizing throws away pixels nobody would see. Heavy compression throws away detail people do see.

So the order is: Image Resizer to the right dimensions, then the Image Compressor to trim the rest.

Sizes that work for attachments and inline images

Which dimensions to use depends on what the recipient does with the image.

For newsletters, keep the whole email under about 1 MB of images. Many people open mail on mobile data, and a 6 MB newsletter loads slowly enough that some of them give up before the first picture appears.

Attachment limits are smaller than they look

Gmail allows 25 MB of attachments per message and Outlook.com around 20 MB. Corporate mail servers are often stricter, 10 MB is common. What catches people out is that attachments are encoded as text when they're sent, which inflates them by about a third. Ten photos at 2.4 MB each look like 24 MB on your computer, and they won't fit under a 25 MB limit once encoded.

Quick rule: keep the total on your disk under about 15 MB if you want it to get through almost anywhere. Ten photos at 300 KB each come to 3 MB, which is nowhere near any limit.

Big attachments also cost the recipient.

Their mailbox fills up, their phone downloads the whole thing on mobile data, and if they forward it to a colleague (which happens more often than you'd think with quotes, photos of damage and property pictures) the same oversized files travel again and land in a second mailbox with its own limits. Why make someone else deal with 30 MB when 3 MB shows the same thing?

Which format to send

JPEG for photos. Always. It's supported by every email client ever made, and at quality 75 to 85 the loss is invisible at screen size.

PNG for screenshots, logos and anything with text or flat colour. A screenshot of a spreadsheet saved as JPEG gets fuzzy halos around every letter, and it's often larger than the PNG anyway. If a PNG screenshot is huge, it's usually because it was taken on a high-resolution display, so halve its dimensions rather than converting it.

WebP is smaller than JPEG at the same quality, and it's great for websites. In email it's a gamble. Several desktop clients, including some versions of Outlook, won't show it inline, and some recipients will get an attachment they can't open. Convert WebP to JPEG before sending.

iPhone photos often arrive as HEIC, which Windows and many webmail viewers don't open reliably. The simplest fix is on the phone itself: set the camera format to "Most Compatible" so it saves JPEG, or share the photo through mail, which converts it on the way out. For WebP, PNG and JPEG, the Format Converter switches between them in the browser.

What I'd do in each case

I tested this on a 4.1 MB photo from a phone, a living room with a window and a lot of fine texture in a rug. At 1600 px wide and quality 80 it came out at 310 KB. At quality 70 it was 240 KB, and I couldn't tell the two apart on a laptop screen. At quality 50 the rug started to look smeared. That's typical: below about 65, savings get small and the damage gets visible.

So my defaults:

• One or two photos to a friend or client: 1600 px long edge, JPEG quality 80. Done.
• A form or portal with a hard limit such as 200 KB or 1 MB: use Compress to a File Size, which hits the target on the actual encoded file instead of making you guess the quality.
• Newsletter images: 1200 px wide, JPEG at 75, and check the total.
• Screenshots: PNG, halve the dimensions if they came from a 4K or Retina screen.

A common mistake is cropping last. If you're going to crop out half the picture, do it before resizing, otherwise you resize pixels you then delete and end up with a smaller image than you meant. Crop in the Image Cropper first, then resize what's left.

Sending a lot of photos at once

Twenty or thirty photos from an event or a property viewing won't fit in one email at full size no matter what you do with the quality slider, because a single phone photo can already be 5 MB on its own.

Resize them.

At 1600 px, they usually will fit: thirty photos at around 300 KB each is about 9 MB. If they won't, split them over two emails rather than compressing everything to quality 40.

Compress to a File Size handles up to five photos per job for free. For a whole folder in one go, batch processing is part of UtiliKit Premium. Either way the photos are processed in your browser and aren't uploaded anywhere, which is worth knowing when they're of someone's home or family.

For other sizes (social posts, website banners, profile pictures) there's a longer list in the UtiliKit guides. For a single email, though, open the Image Resizer, set 1600 px, and you're most of the way there.

More guides

• Getting a Photo Under 50 KB: What to Cut First
• How to Compress an Image to 200 KB for Forms and Uploads
• How to Compress an Image to 100KB Without Ruining It
• Bulk Image Processing Workflow for Websites and Product Photos
• Image Size Cheat Sheet for Websites, Social Media, and Email
• How to Edit Images in Your Browser Without Uploading Files