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Compress Video for Email — Aim at 18 MB, Not 25

Mail servers carry attachments as base64 text, which adds roughly a third to every file on its way out. So this page opens the compressor at 18 MB, which clears a 25 MB inbox limit with room to spare.

Everything happens in this tab. The attachment is never uploaded to a server to be shrunk.

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MP4, MOV, WebM, MKV and AVI, up to 2 GB. The file stays on your device.

Why the target is 18 MB when the limit says 25

SMTP was designed to carry text, and a video is not text. Before an attachment leaves your outbox it is re-encoded into base64, which represents every three bytes of the original as four printable characters. That is a fixed four-to-three expansion — about 33 per cent — and MIME headers plus line breaks push the real figure nearer 37 per cent.

Run it backwards and the answer falls out: 25 divided by 1.37 is a shade over 18. A 25 MB attachment limit is an 18 MB limit measured on your own disk. Compress to exactly 25 MB, as most pages on this subject still advise, and your mail client will cheerfully accept the file before the message bounces somewhere downstream — which is the worst way to find out, because the failure can arrive minutes later.

What each provider really allows

The first table below lists what the providers themselves publish, beside the on-disk size that survives encoding. Two of those figures hide something. Outlook.com's 25 MB covers the entire message — body text, signature images and all attachments together — not 25 MB of video. Yahoo Mail's 25 MB is likewise the sum of every attached file.

Apple is the strict one, capping a message at 20 MB, which leaves roughly 14 MB of file; type 14 into the custom box when that is where the message is headed. Google is the forgiving one: exceed 25 MB and Gmail quietly removes the attachment and substitutes a Google Drive link, which works well enough, provided your recipient can reach Drive at all.

How much clip an 18 MB budget buys

The second table is computed from the compressor's own bitrate curve rather than written by hand, using the bitrate the Balanced preset would pick at each frame size. Attachments tend to be watched once, in a preview pane, on a screen nobody has calibrated, so the honest advice is to spend the budget on length rather than on pixels.

Choosing 720p roughly doubles what fits compared with 1080p and will look identical in an inline player. If the clip still refuses to fit, the answer is not a lower bitrate: below a certain point H.264 stops holding the picture together, and the panel will tell you so rather than hand you something unwatchable.

When a link beats an attachment

Past two or three minutes, a share link wins on every measure. Google Drive, OneDrive and Dropbox all give the recipient the original file at full quality and cost the mailbox nothing, and Apple's Mail Drop does the same for files up to 5 GB, straight from Mail or iCloud.com, without counting against your iCloud storage.

The one case where an attachment still wins is a recipient whose employer blocks file-sharing domains, which happens often enough on tightly managed corporate networks to be worth asking about before you send. That is the situation this page exists for: when it has to be an attachment, 18 MB is the number that gets through.

Attachment limits, and what they mean on disk

Published limits apply to the encoded message. The middle column is what you should actually compress to.

ServicePublished limitSafe size on diskIf it is too big
Gmail25 MB per message18 MBThe attachment is swapped for a Google Drive link automatically.
Outlook.com25 MB for the whole message18 MBMicrosoft steers you towards a OneDrive link instead.
Yahoo Mail25 MB of attachments in total18 MBThe message is refused outright; use a share link.
iCloud Mail20 MB per message14 MBMail Drop carries up to 5 GB and keeps it for thirty days.
Last checked: September 2026Gmail Help: send attachmentsMicrosoft: sending limits in Outlook.comYahoo Help: message size limitsApple Support: iCloud message limits

How much video fits in 18 MB

Using the bitrate the Balanced preset would choose at each frame size, keeping a 128 kbps audio track. These figures come out of the tool, not out of a copywriter.

Frame sizeFits in 18 MB30 fps
1080p38 s3.7 Mbps
720p1:161.8 Mbps
480p2:27868 kbps

An iCloud Mail recipient leaves you only 14 MB, so take roughly a fifth off each of these lengths when that is the destination.

Getting a video small enough to attach

Three steps, entirely inside this tab

  1. Choose the video

    Drag in the file you meant to attach. It is read locally by the browser and stays on your machine from start to finish.

  2. Leave the target at 18 MB

    That is a 25 MB inbox limit minus what base64 adds along the way. Set 14 MB instead if the message is going to an iCloud Mail address.

  3. Save it and attach

    Download the compressed MP4 and attach it the way you always would. Nothing is watermarked, and the name stays close to the original.

FAQ

Email attachments and video size

Because the 25 MB is measured after encoding, not before. Attachments travel as base64, which turns every three bytes into four characters — a 33 per cent increase before MIME headers add a little more. Twenty-five divided by 1.37 is a shade over 18, so 18 MB on disk is what actually fits.
All three publish 25 MB, though Outlook.com and Yahoo Mail count the whole message — body, signature images and every file together — rather than one attachment in isolation. The table on this page lists each published figure next to the on-disk size that survives the trip.
Apple caps incoming and outgoing messages at 20 MB, which works out at roughly 14 MB of file once encoding overhead is accounted for. Type 14 into the custom box. Anything larger has to go through Mail Drop, which handles up to 5 GB and holds it for thirty days.
Drop to 720p first: it roughly doubles the length that fits and looks the same in a mail client's small inline player. If it still will not go, trim the clip, or send a Drive, OneDrive or Mail Drop link — the recipient then gets the original at full quality.
The video and audio are both re-encoded, so fine detail and fast motion lose a little, and the output is always MP4 with H.264 and AAC inside. Rotation and duration are preserved. Nothing is added: no watermark, no overlay, no appended promotional frame.
It does not. The browser decodes and re-encodes the video on your own hardware, and no request carrying the file is ever made — open the Network panel in your developer tools and watch if you would like to confirm it. There is no account and no queue.

Related tools

Other ways to make a video smaller, and the one thing shrinking cannot fix.

Bitrate you spend is gone for good. When an old clip is simply too soft to send at any size, rebuild it with the AI video upscaler

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