How to compress a video for email: size limits, bitrate math and settings
9 min read · Updated 23 October 2026
How do I compress a video for email? Find your email service's attachment limit, set a target size a few megabytes below it, then re-encode the video at a lower bitrate and, for long clips, a lower resolution. Gmail and Outlook.com both cap a message at 25 MB, so a target of about 18 to 20 MB is a safe choice. You can do this in your browser with the video compressor set for email, which works out the bitrate for you.
Phone videos are huge. A one minute clip from a modern phone can easily run past 100 MB, and email was never designed for files that big. This guide gives you the real limits, the math behind them, and a simple way to choose settings so the video still looks fine when it arrives.
The attachment limits that matter
Different services set different caps. These are the ones most US readers run into.
| Service | Limit | Notes |
|---|---|---|
| Gmail (personal) | 25 MB per message | If the files are too big, Gmail swaps them for a Google Drive link |
| Outlook.com | 25 MB per message | Counts text, inserted files and attached files together |
| Microsoft 365 work or school | 35 MB for sending by default | An administrator can set it between 1 MB and 150 MB |
| Apple Mail with Mail Drop | Up to 5 GB | Files are available to the recipient for 30 days |
| Google Workspace work or school | Set by the administrator | No fixed default |
Sources are the Gmail help page, Microsoft's Outlook.com help page, Microsoft's Exchange Online limits page and Apple's Mail Drop page. Limits change, so check your own provider if the message bounces.
Three points about those numbers:
- The limit is per message, not per file. Two 15 MB videos in one email add up to 30 MB, and that is too big for Gmail.
- Email adds weight. Attachments are converted to text so they can travel inside a message, and that makes them roughly one third bigger. Microsoft's own documentation mentions a 33 percent increase for messages that leave its servers. Google does not publish exactly how it counts the size, so the safest plan is to leave room. A video of 18 MB becomes about 24 MB after the encoding increase, which still fits under 25 MB.
- The recipient matters too. Their provider might have a lower limit than yours. A work account with a 10 MB cap will reject a 20 MB video even if you sent it from Gmail.
When to skip compression and send a link
If the video is long, compressing it enough to fit in an email may ruin it. A 20 minute clip squeezed to 18 MB will look terrible. In that case:
- Gmail can add a Google Drive link automatically when attachments are over the limit.
- Outlook.com lets you share a OneDrive link, and linked files do not count toward the 25 MB limit.
- Apple Mail can use Mail Drop for files up to 5 GB.
A link also keeps the original quality. Compress only when the recipient needs a small file they can open straight from the message.
The bitrate math
A video file is mostly the video stream plus a smaller audio stream. File size follows one rule:
size = bitrate x duration
Bitrate is how many bits per second the encoder spends. To work out the bitrate you can afford, flip it around:
- Convert the target size to bits. 1 MB is 1,048,576 bytes and each byte is 8 bits. So 18 MB is 18 x 1,048,576 x 8 = 150,994,944 bits.
- Divide by the duration in seconds to get the total bits per second.
- Take off about 2 percent for the file container's overhead.
- Subtract the audio. 128 kb/s is a common audio bitrate for AAC.
- What remains is the video bitrate.
The compressor does all five steps when you give it a target size. Here is what they look like for an 18 MB target and 128 kb/s audio:
| Video length | Total bitrate | Left for video |
|---|---|---|
| 1 minute | about 2,517 kb/s | about 2,338 kb/s |
| 2 minutes | about 1,258 kb/s | about 1,105 kb/s |
| 3 minutes | about 839 kb/s | about 694 kb/s |
| 5 minutes | about 503 kb/s | about 365 kb/s |
| 10 minutes | about 252 kb/s | about 119 kb/s |
The pattern is clear. Double the length and you halve the bitrate each second of video gets. Past about five minutes the video stream gets so little data that the picture falls apart, unless you also lower the resolution.
A worked example
Take a 2 minute clip from your phone that you want to email through Gmail.
- The Gmail limit is 25 MB, so the plan is a 20 MB target. (Use 18 MB if you want extra room for the one third increase from encoding.)
- The compressor's own example for this length: 20 MB is 20 x 1,048,576 x 8 = 167,772,160 bits. Divide by 120 seconds and you get about 1,398 kb/s in total.
- Keep 2 percent for the container and subtract 128 kb/s of audio. That leaves about 1,242 kb/s for the video.
- That is a workable bitrate at 720p, but thin for 1080p. Setting the maximum resolution to 720p is a good idea.
Now the same video at 5 minutes. A 20 MB target leaves about 420 kb/s for the video. At 1080p that is likely to look blocky. Drop the resolution to 480p, or split the clip into two shorter videos and send them in two emails.
Step by step in the browser
- Open the video compressor for email. It opens in target size mode with 20 MB preset. You can add up to 20 videos, and MP4, MOV, WebM and MKV files are accepted.
- Change the number to match your limit. For Gmail or Outlook.com, 20 MB or less is a good target. For a 10 MB work account, enter 8 or 9.
- If the video is longer than a couple of minutes, lower the Maximum resolution. You can also lower the frame rate.
- Select Compress. The page shows each file's estimated output size.
- Download the smaller file and check that it plays properly before you attach it.
The general video compressor offers the same controls, plus quality presets, and lets you lower the audio bitrate too. Everything runs on your device, so the video is not uploaded.
What if the result is still too big?
Encoders do not hit a target exactly, because they spend more bits on busy scenes and fewer on calm ones. The tool handles this by encoding a second time at a lower bitrate if the first result is over the target. If it is still over, the page says so. Then lower the resolution or the frame rate, or set the target a few megabytes lower, and run it again. Very grainy footage, such as a dark room at night, is the hardest to shrink.
Choosing a resolution
Resolution is the pixel size of each frame. Fewer pixels means each one can get more bits, so a smaller frame often looks cleaner than a large one at the same file size.
| Resolution | Pixels per frame | Good for |
|---|---|---|
| 1080p (1920 x 1080) | about 2.1 million | Short clips of one or two minutes |
| 720p (1280 x 720) | about 0.9 million | Most clips up to about five minutes |
| 480p (854 x 480) | about 0.4 million | Long clips, or when the file must stay very small |
This is a rule of thumb, not an official standard: if the bitrate left for the video falls below roughly 500 kb/s, step down one resolution. On a small phone screen, 720p and even 480p look fine for casual videos.
iPhone and Android tips
- iPhone: In the Mail app, attaching a large video may offer Mail Drop automatically. To shrink the video first, use the browser compressor from Safari. Choose the video from your photo library when the page asks for a file.
- Android: Gmail adds a Drive link when you go over the limit. If the recipient needs an actual file, compress first with the browser tool.
- Trim first. Cutting the start and end of a clip is the easiest size reduction there is. A 90 second video that could be 45 seconds should be shortened before you compress anything.
Common mistakes
- Aiming right at the limit. A 24.8 MB file can still fail once encoding overhead is added. Leave a few megabytes of room.
- Forgetting the other attachments. The limit covers the whole message, including photos, PDFs and the signature image.
- Resizing in the email program. Microsoft notes that resizing an image does not reduce its file size in Outlook.com. Compress the file itself before attaching it.
- Compressing twice. Each re-encode loses detail. Keep the original, and compress from it each time.
- Keeping 1080p for a long video. A long clip at 1080p with a small target looks worse than the same clip at 720p.
- Sending an unwatchable result. Always play the compressed file once before you send it.
- Ignoring the recipient's limit. Ask or check if you are sending to a company address.
FAQ
What size should a video be to email? Under the limit of the weakest link. For Gmail and Outlook.com that is 25 MB, so aim for 18 to 20 MB. For a work address, ask for the limit or aim below 10 MB.
Will compression make my video look worse? Yes, some. The encoder spends fewer bits, so fine detail is lost. Lowering the resolution to 720p or 480p keeps long videos clearer than leaving them at full size.
Why does my video say it is under 25 MB but Gmail still rejects it? Other attachments and the message text count toward the total, and encoding makes attachments larger on the wire. Compress to a lower target, such as 18 MB, and try again.
Can I email a video longer than 10 minutes? Not in good quality at 25 MB. The math above shows only about 119 kb/s is left for the video at 10 minutes and an 18 MB target. Send a Drive, OneDrive or Mail Drop link instead.
Is it safe to compress a private video online? The toolsdocks compressor runs in your browser, and the video stays on your device. Many other sites upload your video to their servers, so check before using one for private footage.
Which format should I use for email? MP4 plays almost everywhere, so choose MP4 output. WebM is available but is less universal for people who open attachments on older devices.
For converting a video that will not play, see our video converter, and for pulling just the sound out of a clip, read how to extract audio from a video.