How to Reduce a Video's File Size

Three settings decide the size

Resolution is the number of pixels in each frame, such as 1080p or 720p. Fewer pixels means less to store. This is usually the single most effective setting, as 720p has less than half the pixels of 1080p, and on a phone screen it can look almost the same.

Bitrate is how much data is used per second of video, usually in megabits per second (Mbps). It is the setting that most directly controls file size. Lower it too far, however, and you will see blocks and smears, especially in fast movement.

Frame rate is the number of pictures per second, typically 24, 30 or 60. Dropping from 60 to 30 can save space on video of fast action, and most ordinary footage looks fine at 30. Choosing a higher value than the original adds nothing, as new detail cannot be created.

A simple formula for estimating size

File size is close to bitrate multiplied by duration. Because bitrate is measured in bits and file size in bytes, you divide by 8. Add the audio bitrate too, which is usually small by comparison. So for a one-minute clip with 2 Mbps of video and 128 kbps of audio, the total is about 2.13 Mbps. Multiplied by 60 seconds and divided by 8, that comes to roughly 16 MB.

This also works backwards, and that is the useful part. If a video has to fit under 25 MB and lasts 2 minutes, you have 200 megabits to spend over 120 seconds, or about 1.6 Mbps in all. Leave some room for audio, and aim for around 1.4 Mbps of video.

Under 10 MB
Under 16 MB
Under 25 MB
Under 50 MB

about 1.2 Mbps
about 2 Mbps
about 3.2 Mbps
about 6.5 Mbps

Reduce a video in three steps

Video Converter lets you change these settings along with the format. Long files take a while, as every frame has to be processed on our server.

1. Open Video Converter, upload your video and choose MP4 as the output.
2. Set a lower resolution, such as 720p, and if needed, enter a bitrate based on the formula above.
3. Convert it, download the result, and check both the file size and how it looks on the device people will use.

Which settings suit which situation?

For sending to friends over messaging, 720p at around 2 Mbps usually gives a good balance. Messaging apps may re-compress videos sent in the normal way, so a much better picture will not always survive. Sending as a document keeps your file as it is, though apps set limits that change from time to time.

For email, the usual attachment limit is about 25 MB for Gmail and many others, so a short clip at 480p or 720p with a low bitrate can fit. For anything longer, a shared link from Google Drive or YouTube is more practical, and it saves your recipient from a large download.

For a website, use MP4, and consider a lower resolution for visitors on phones. For keeping a family video, do not compress the only copy at all. Storage is cheap, and detail once discarded is gone forever, so keep the original and make a smaller copy for sharing.

Choosing the right format

MP4 with H.264 is the safest choice: it plays on phones, computers, TVs and websites, so use it unless you have a specific reason not to. MOV files from iPhones can be converted to MP4 when someone on Windows cannot open them. AVI and older formats can often be made far smaller simply by converting to MP4, as they tend to use old, less efficient compression.

WebM is a good format for web pages. MKV is popular for films with several audio or subtitle tracks, but phones and TVs do not always accept it. Changing format alone is no guarantee of a smaller file, as size depends mostly on bitrate and resolution, so set those too.

Mistakes to avoid

Do not raise the resolution in the hope of improving quality. A 720p clip converted to 4K keeps the same detail, spread across more pixels, in a far bigger file. Similarly, each round of compression loses some quality, so go back to the original every time rather than compressing a compressed copy, as damage builds up.

Avoid setting the bitrate too low for the content. A talking head against a plain wall can look fine at 1 Mbps, whereas sports or handheld footage at the same bitrate falls apart into blocks, because every pixel is changing. Test a short section before you process a long video, so you do not spend time on settings that turn out to be wrong.

Remember that a ZIP will not help, as video files are already compressed and barely shrink further. To cut size beyond these settings, trim the clip, because a shorter video is always smaller. Your phone's built-in editor can trim a video in seconds before you upload it here.

Why audio matters less, and when it matters more

Audio takes only a small slice of most files, typically 128 kbps compared with several thousand for the video, so reducing it will not save much. Keep it at a decent level, as poor sound is often more annoying than a slightly soft picture.

The exception is when the picture hardly matters, as in a recorded lecture or webinar, where people mainly listen. A low resolution and low bitrate are enough for slides, and they can reduce a long recording dramatically. Audio Converter handles audio files, so if you already have the sound as a separate file, an MP3 may be all your audience needs.

Check before you send

Watch the first few seconds and a fast-moving part of the result on the device your viewer will use, and listen to confirm that the sound is still in sync. Then check the actual file size against the limit. If it is slightly over, reduce the bitrate a little and convert again from the original.