A video's file size comes down to two things: how much data it uses per second (its bitrate) and how long it is. Phones record at high resolutions and bitrates, so even a short clip can be too big for an email attachment. To make it fit, cut it to the part you need, then compress it to a lower resolution and bitrate. If it still won't fit, or the quality matters more than the convenience of an attachment, send a link instead. Below are the limits to aim for and the order that wastes the least time. Video Cutter and Compress Video both run in your browser, so the video isn't uploaded while you do it.
What decides a video's file size
The basic formula is simple: size ≈ total bitrate × duration. Bitrate is usually given in megabits per second (Mbps), and there are 8 bits in a byte. So a video at 10 Mbps takes 10 × 60 ÷ 8 = 75 MB per minute. Bring that down to 2 Mbps and the same minute is 15 MB.
MDN's guide to video codecs lists what pushes the size up:
- Resolution. “The higher the resolution of a video, the larger it gets.” A 1080p frame has about 2.07 million pixels; 720p has about 0.92 million, less than half.
- Bitrate and quality settings. “Higher bit rates inherently lead to larger output files,” and higher quality settings generally do too.
- Frame rate. Higher frame rates cause larger files, assuming the frame rate isn't reduced during encoding.
- Motion. Compression works by recording the differences between frames, so the more motion there is, the larger the output tends to be. A screen recording shrinks far more than handheld footage of a football game.
Of these, you control three: length (by trimming), resolution and bitrate (by compressing). The audio track adds a little too. Compress Video encodes audio at 128 kbps, which is 128 × 60 ÷ 8 = 960 kB, or about 1 MB per minute.
Email attachment limits
- Gmail. Google's help page says the limit for personal Gmail accounts is 25 MB. If your attachments are bigger, Gmail automatically removes them and adds a Google Drive link to the email instead. For work and school accounts, the Google Workspace administrator sets both the sending and the receiving limits.
- Outlook. Microsoft's support article for Outlook 2013 and later says Outlook has a default limit of 20 MB for Internet email accounts (POP3, IMAP), counting all attachments in a message together. With a Microsoft Exchange mailbox the default is 10 MB, set by the Exchange administrator. When a file is too big, Outlook suggests putting it in a shared location and sending a link.
- Apple Mail. Mail Drop sends attachments of up to 5 GB through iCloud from Mail on a Mac, iPhone or iPad, and from iCloud.com. According to Apple, recipients have 30 days to download them, and they don't count against your iCloud storage.
Other providers have their own numbers, so check yours. The receiving side can have a limit too, which is why it's sensible to aim a little under the limit rather than right at it.
How small does it need to be?
Turn the formula around to see what total bitrate a video can have and still fit. Here it is for a 25 MB target, counting 1 MB as 1,000,000 bytes:
| Length | Total bitrate that fits in 25 MB |
|---|---|
| 30 seconds | about 6.7 Mbps |
| 1 minute | about 3.3 Mbps |
| 2 minutes | about 1.7 Mbps |
| 5 minutes | about 0.67 Mbps |
Subtract about 0.13 Mbps for the audio and you have what's left for the picture. A 30-second clip has plenty of room. At five minutes, there's very little left to describe each frame, so expect to drop to 480p, trim the video, or send a link.
Step 1: cut what you don't need
Trimming is the one change that costs nothing in quality. In Video Cutter, set the start and end on the preview timeline. The default fast mode copies the video without re-encoding, so the quality stays the same and the file shrinks roughly in proportion to the length you keep: 30 seconds out of a 5-minute video is about a tenth of the size. Fast mode cuts on keyframes, so the clip may start a moment before the point you picked; turn on Exact cut if the first frame matters, which re-encodes the video.
The cutter keeps one continuous section. Trim first, then compress the trimmed file, so the video is compressed only once.
Step 2: compress
Compress Video has two settings:
- Quality: Smaller file, Balanced (the default) or Better quality. This sets how far the bitrate is lowered.
- Max resolution: Original, or 1080p, 720p and 480p where they're smaller than the video. The default steps down from large videos: anything taller than 1080 pixels starts at 1080p, and anything taller than 720 pixels starts at 720p. The setting is a maximum, so nothing is ever enlarged.
The result is an MP4 file with 128 kbps audio. The video is encoded as H.264 when your browser can produce it, and otherwise with the next codec it supports. After compressing, the page shows the original and new size side by side, so you know straight away whether it fits.
If it doesn't, try these in order, always starting again from the original file:
- 720p with Balanced.
- 480p with Balanced, or 720p with Smaller file. Lowering the resolution often looks better than squeezing the bitrate hard at a higher resolution.
- 480p with Smaller file.
- If that's still too big, trim more or send a link.
Every compression pass is lossy: fine detail, grain and fast motion suffer first. Compressing a copy that was already compressed adds a second round of loss, which is why you should go back to the original each time. Everything happens in your device's memory, so a long 4K video may be too much for a phone browser; a computer handles it more reliably.
When a link is the better choice
Sometimes the right answer is not to attach the video at all:
- The video is long, or the quality matters, such as a recording of a performance or footage someone will edit.
- Several people need it, and you don't want a large attachment copied into every mailbox.
- You'd have to compress it so hard that it's no longer worth watching.
Gmail already turns oversized attachments into Google Drive links, Outlook suggests sharing from a shared location, and Mail Drop sends a link that lasts 30 days. A link keeps the original quality. Before sending it, check who the link is shared with, especially for private videos.
Why compress in the browser
The videos people need to send are often personal: family clips, a recorded interview, footage for work. Compress Video and Video Cutter process the file inside your browser tab, so it isn't sent to a server and there is no upload to wait for before the work even starts.