Why is my video file so big?

A video's size comes down to one sum: how much data it uses each second, multiplied by how many seconds long it is. The data per second is called the bitrate. Everything else, like resolution and frame rate, matters because it changes the bitrate.

The sum behind every video

Bitrate is measured in megabits per second (Mbps). There are 8 bits in a byte, so a video uses its bitrate divided by 8 in megabytes every second. Over a minute, that adds up quickly:

Space used by one minute of video at different bitrates
Bitrate	Each second	One minute
5 Mbps	0.625 MB	37.5 MB
10 Mbps	1.25 MB	75 MB
20 Mbps	2.5 MB	150 MB
50 Mbps	6.25 MB	375 MB

So a 2 minute clip recorded at 20 Mbps is about 300 MB, far past the limit of most apps and email.

What pushes the bitrate up

Resolution. 4K has four times as many pixels as 1080p, so it needs much more data to stay sharp.
Frame rate. 60 frames per second shows twice as many pictures as 30. It needs more data, though usually not quite double, because frames next to each other are similar.
Movement. Fast action, shaky footage, water, crowds and confetti change a lot from frame to frame and need the most data. A steady shot of a still scene needs the least.
The format. Newer formats like HEVC need noticeably less data than the older H.264 for a similar picture, which is one reason the same clip can be different sizes on different devices.

Phones record with plenty of data to spare, so the video still looks good after editing. That is great for quality and the reason the files are so large.

Sound is a small part

Sound usually takes up much less room than the picture. At 128 kbps, a common setting, it uses about 1 MB per minute. Removing the sound barely changes the size of most videos.

How to make it smaller

Because size is bitrate times length, there are only two levers: use less data per second, or make the video shorter.

Lower the data per second. This is what a compressor does. To keep a small file looking clean rather than blocky, it also lowers the resolution when it has to.
Make it shorter. Trimming a 60 second clip to 30 seconds halves the size at the same quality, or doubles the quality at the same size.

To give a sense of the trade-off, this is how long a widescreen video can be at 25MB before the compressor steps down to each resolution:

Longest 16:9 clip that stays at each resolution at 25MB
Resolution	Up to
1080p	42 seconds
720p	93 seconds
480p	3.5 minutes
360p	5.5 minutes

The size guide has the same numbers for other sizes.

Shrink a video to the size you need →