Every video app throws around numbers like 720p, 1080p and Mbps as if they explain the file size on their own. They do not, not by themselves. Resolution (720p, 1080p) is the picture size.

Bitrate is the thing that actually decides how many megabytes that picture costs you per second. Here is the arithmetic, with real numbers, so you can work out a video’s size before you record or send it, not after.

Short answer

What “Bitrate” and “720p” Actually Mean for Your Video’s File Size
  • Bitrate is how many bits the video spends per second. More bits per second, bigger file, same length.
  • 720p just means the picture is 1280 by 720 pixels. It does not fix a size on its own, bitrate does that.
  • File size = bitrate × length in seconds ÷ 8. That is the whole formula.
  • At YouTube’s own recommended 720p bitrate, one minute of video is already bigger than Gmail’s 25 MB attachment limit.

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YouTube’s own recommended upload bitrates by resolution, standard dynamic range. Source: Google/YouTube Help, “Recommended upload encoding settings,” read 5 Nov 2026.
Resolution YouTube’s recommended bitrate (standard frame rate) Recommended bitrate (48–60 fps)
360p 1 Mbps n/a
480p 2.5 Mbps n/a
720p 5 Mbps 7.5 Mbps
1080p 8 Mbps 12 Mbps
1440p 16 Mbps n/a
2160p (4K) 35–45 Mbps n/a

The formula, and what it means in practice

File size in megabytes works out to bitrate in megabits per second, times the length in seconds, divided by 8 (there are 8 bits in a byte). That is the entire calculation. Plug in a bitrate from the table above and a clip length, and you get a real size, no app required.

Video-only size, calculated from the formula above. Add roughly 1–3 MB per minute for stereo audio on top of these numbers.
Resolution Bitrate used Length Arithmetic Size (video only)
720p 5 Mbps (YouTube standard rate) 30 s 5 × 30 ÷ 8 18.75 MB
720p 5 Mbps (YouTube standard rate) 60 s 5 × 60 ÷ 8 37.5 MB
1080p 8 Mbps (YouTube standard rate) 30 s 8 × 30 ÷ 8 30 MB
1080p 8 Mbps (YouTube standard rate) 60 s 8 × 60 ÷ 8 60 MB

Worked examples

The same four clips measured against Gmail’s 25 MB attachment ceiling (source cited in the email-a-large-video post).
Clip Size (video only) Fits Gmail’s 25 MB limit?
30 s at 720p 18.75 MB Yes, with little headroom once audio is added
60 s at 720p 37.5 MB No
30 s at 1080p 30 MB No
60 s at 1080p 60 MB No

Notice what that means next to Gmail’s 25 MB attachment limit, covered in emailing a large video from iPhone: a one-minute clip encoded at YouTube’s own recommended 720p bitrate is already over that ceiling, on video alone, before audio is added. That is arithmetic, not a guess about any one app’s actual output.

Why your iPhone’s own video is usually smaller than this table

These are YouTube’s upload recommendations for a finished, re-encoded file meant to look clean at any screen size on their platform, not a measurement of what an iPhone records or what Grabio outputs.

Apple’s own camera uses its own bitrate choices per resolution and frame rate, shown to you directly in Settings, Camera, Record Video next to each option. That is the one place to see a true, current number for your own device, because it varies by iPhone model and iOS version.

What stays true regardless of whose encoder made the file: the formula above, and the fact that halving the bitrate roughly halves the file size at the same length and resolution. That is the lever behind compression. For the practical, step-by-step version of pulling that lever on a video already sitting in your library, see reducing a video’s file size on iPhone.

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Bitrate and file size: FAQ

Is 720p always a smaller file than 1080p?

At the same bitrate, yes, because 1080p has more pixels to describe per frame and typically gets allotted more bits. But the two numbers are independent: a 720p file encoded at a high bitrate can still beat a 1080p file encoded at a low one.

What is the actual formula for file size?

Bitrate in megabits per second, multiplied by the length in seconds, divided by 8 to convert bits to bytes. That gives you megabytes.

Does frame rate change the bitrate I need?

Yes. More frames per second means more pictures to encode every second, so a 60fps clip needs a noticeably higher bitrate than a 30fps clip at the same resolution to look equally clean, per YouTube’s own recommended figures above.

Where do I see my iPhone’s actual recording bitrate?

Settings, Camera, Record Video lists an approximate size per minute next to each resolution and frame rate option. That is the real number for your specific phone, not a general table like this one.

Does this table describe what Grabio outputs?

No. It is YouTube’s own published recommendation for uploads, used here only to do the arithmetic. Grabio’s 720p compress uses its own settings, not measured in this post.