Video file size calculator

File size is bitrate multiplied by duration. Give this two of the three and it returns the one you are missing, along with the resolution the result can realistically carry.

What do you want to work out?
Enter a duration to see the result.

The arithmetic, if you would rather do it yourself

There is nothing clever happening here, but the units have to be kept straight. A megabyte on this page is 1,048,576 bytes — the binary one, which is what your operating system, Discord and a mail server all count with. A kilobit per second is 1,000 bits per second, the decimal one, which is what every encoder means by kbps. Mixing the two is a 2.4 percent error, so the conversion below goes through bits rather than pretending a kilobit and a kibibyte cancel. 

total_kbps = target_MB × 1,048,576 × 8 / duration_seconds / 1000
audio_kbps = 64 if total_kbps < 400, else 96 if total_kbps < 900, else 128
video_kbps = floor(total_kbps × 0.96 − audio_kbps)

file_MB    = (video_kbps + audio_kbps) × 1000 × duration_seconds
             / 8 / 0.96 / 1,048,576

The 0.96 is headroom for container and muxing overhead — the bytes that describe the file rather than the picture. It is a small share, but on a tight budget against a hard limit it is the difference between fitting and not.

The audio allowance scales with the budget rather than sitting at 128 kbps, because a budget that only affords 200 kbps in total cannot spend most of it on sound. That is the rule the compressor itself applies, and this page calls the same function to get it, so the two cannot drift apart.

Bitrate reference by size and length

Video bitrate available at each combination, in kbps, with the audio allowance already subtracted. Read down a column to see how quickly a fixed budget thins out as a clip gets longer.

Length 8 MB16 MB25 MB50 MB100 MB250 MB
30 seconds 2,019 1080p 4,166 1080p 6,582 1080p or original 13,293 1080p or original 26,715 1080p or original 66,980 1080p or original
1 minute 945 720p 2,019 1080p 3,227 1080p 6,582 1080p or original 13,293 1080p or original 33,426 1080p or original
2 minutes 440 480p 945 720p 1,549 720p 3,227 1080p 6,582 1080p or original 16,649 1080p or original
5 minutes 150 360p 333 360p 575 480p 1,214 720p 2,556 1080p 6,582 1080p or original
10 minutes — 150 360p 271 360p 575 480p 1,214 720p 3,227 1080p
30 minutes — — — 159 360p 351 360p 990 720p

The second line in each cell is the largest resolution that bitrate realistically carries on ordinary H.264 footage. A dash means the budget falls under 150 kbps, which is too little for the encoder to hold a picture together at any resolution — the compressor reports the same verdict for those inputs. Trim the clip instead.

What bitrate each resolution wants

These are H.264 starting points for ordinary footage, not rules. Screen recordings and talking heads sit comfortably below the ranges; sport, film grain, water and confetti need the top of them or more.

  • 360p — 300 to 700 kbps
  • 480p — 600 to 1,500 kbps
  • 720p — 1,500 to 3,500 kbps
  • 1080p — 3,500 to 6,500 kbps
  • 1440p — 6,000 to 12,000 kbps
  • 4K — 12,000 to 25,000 kbps

These ranges and the resolution the calculator names above are answering two different questions, and it is worth being explicit about the gap. The calculator names the highest resolution a budget still holds together at — 2,000 kbps is where 1080p stops falling apart. The list here is where each resolution starts looking good — 1080p at 2,000 kbps is watchable and visibly compressed. If a size limit hands you a number below the range for your resolution, the answer is to drop a resolution step rather than to accept the bitrate. The bitrate guide explains why the relationship is not linear, and the bitrate calculator adjusts these ranges for frame rate, content and codec.

Questions

How do I calculate video file size from bitrate?

Multiply the total bitrate in kilobits per second by 1,000 and by the duration in seconds to get bits, divide by 8 for bytes, then by 1,048,576 for megabytes. A 2,000 kbps video running 60 seconds is 120,000,000 bits, which is 15,000,000 bytes, or 14.31 MB. Remember to include the audio: at 128 kbps of AAC, and allowing 4 percent for container overhead, the same clip lands at 15.85 MB. This page counts a megabyte as 1,048,576 bytes throughout, which is what the operating system and every upload limit mean by it.

What bitrate do I need for 1080p?

For general footage, roughly 4,000 to 6,000 kbps with H.264 gives a comfortably good 1080p picture. Static content such as a screen recording or a slide deck holds up far lower, often around 1,000 kbps, because most of the frame does not change. Sport, grain and confetti need more than the top of that range. The resolution this calculator names for a budget is the floor of that: the point below which 1080p stops holding together on ordinary footage, which is around 2,000 kbps, not the point at which it looks good.

Why is my compressed file bigger than the calculator says?

Container and muxing overhead adds a few percent, and rate control is a prediction rather than a guarantee — an encoder aiming at a bitrate can land above it on footage it finds hard. Leave 5 to 10 percent of headroom against any hard limit.

Related tools

Skip the arithmetic entirely

The compressor does all of this for you: choose target-size mode, type the ceiling, and it solves the bitrate from the clip length, encodes locally, then measures the result and corrects itself if it overshot.

Compress to a target size