Video Bitrate & File Size Calculator
File size, bitrate or duration — plus what the resolution actually needs.
How it works
The arithmetic is one line: file size in bytes is total bitrate times duration divided by eight. A 1 hour 30 minute video at 8000 kbps video plus 192 kbps audio comes to about 5.5 GB, and the only subtlety is that bitrates are quoted in bits while file sizes are in bytes.
What bitrate a given resolution needs is the real question, and bits per pixel is the honest way to think about it. 1080p at 30 fps is about 62 million pixels a second; 8000 kbps over that is roughly 0.13 bits per pixel, which is a normal figure for H.264 on ordinary content. Below about 0.08 the encoder starts visibly giving up — blocking in shadows, smearing on motion, banding on gradients.
Two things change the requirement more than resolution does. Frame rate is linear-ish: 60 fps needs roughly 1.5 times the bitrate of 30, not double, because consecutive frames are more similar. And content matters enormously — a talking head at 1080p is comfortable at 3000 kbps while grass, confetti, water or film grain at the same resolution can consume three times that, because they are close to incompressible.
Codec generation is worth a lot. H.265 delivers roughly the same quality as H.264 at about 50% of the bitrate, and AV1 slightly better again, at the cost of encode time and older-device compatibility. ProRes is not in that comparison at all — it is an intermediate codec that deliberately spends bitrate to stay easy to edit, which is why it runs into the hundreds of megabits.
If quality rather than size is the goal, do not use bitrate at all. Use constant quality mode — CRF in x264 and x265 — which spends bits where the picture needs them and lets the file size land where it lands. Fixed bitrate exists for streaming, where the pipe is the constraint, not the picture.
Common questions
What bitrate for 1080p?
3000–6000 kbps in H.264 for ordinary content, 8000 or more for high motion, half of that in H.265. Streaming platforms publish their own targets and re-encode everything you send anyway, so upload above their target and let them do the work.
Why is my file bigger than calculated?
Container overhead is a percent or two, and a variable-bitrate encode will exceed its average target on demanding passages unless capped. If it is dramatically over, the encoder was probably in constant-quality mode, where the bitrate setting is only a ceiling.
H.264 or H.265?
H.265 for storage and archive — about half the size at the same quality. H.264 for compatibility, because it plays everywhere including hardware a decade old. AV1 is better again and royalty-free, but encoding is slow and support on older devices is patchy.
Should I target a file size at all?
Only when something imposes one — a disc, an upload limit, a bandwidth cap. Otherwise use constant quality mode, which spends bits where the picture needs them. Forcing a fixed bitrate wastes them on easy scenes and starves the hard ones.