How the math works
Video file size has nothing to do with resolution directly — it is simply bitrate × duration. Bitrate is measured in bits per second, and there are 8 bits in a byte, so:
File size (bytes) = (video bitrate + audio bitrate in bits/s) × duration in seconds ÷ 8
Resolution and frame rate matter indirectly: the more pixels you push per second, the more bitrate you need for the image to look clean. That is why the presets above pair each platform and resolution with a recommended bitrate rather than a fixed file size.
Recommended upload bitrates (H.264, SDR)
| Use case | Resolution / fps | Recommended bitrate | ≈ Size per 10 min |
|---|---|---|---|
| YouTube | 1080p 24–30 | 8 Mbps | 0.61 GB |
| YouTube | 1080p 50–60 | 12 Mbps | 0.91 GB |
| YouTube | 4K 24–30 | 35–45 Mbps | 2.6–3.4 GB |
| YouTube | 4K 50–60 | 53–68 Mbps | 4.0–5.1 GB |
| Twitch live (OBS) | 1080p60 | 6 Mbps (ingest cap) | — live |
| Instagram Reels | 1080×1920 | ~5 Mbps | 0.38 GB |
| Client review copy | 1080p | 10 Mbps | 0.75 GB |
Platform recommendations change over time — always check the current spec for contractual deliveries. Broadcast and archival codecs (XDCAM, ProRes, DNxHD) use fixed bitrates set by the codec profile, not by you.
Streaming: pick bitrate from your upload speed
For live streaming in OBS, your bitrate is limited by your internet upload speed, not by quality preferences. A safe rule: total bitrate ≤ 70% of your measured upload speed. On a 10 Mbps upload connection, that means streaming at 6 Mbps is the practical ceiling — which conveniently matches Twitch's standard ingest cap. If your upload is slower, drop resolution before you drop frame rate: 900p60 at 4.5 Mbps almost always looks better in motion than 1080p60 starved at the same rate.
Delivering to a size limit
Switch the calculator to Target size → bitrate mode when a platform or client gives you a hard cap — an email attachment limit, a festival upload portal, a 4 GB card. Enter the duration and target size and you get the video bitrate to type into your encoder. Leave ~5% headroom below hard limits to cover container overhead.
FAQ
How do I calculate video file size from bitrate?
File size = (video bitrate + audio bitrate) × duration ÷ 8. Bitrate is measured in bits per second, so dividing by 8 converts it to bytes. Example: a 10-minute video at 8 Mbps video + 320 kbps audio is (8,000,000 + 320,000) × 600 ÷ 8 ≈ 624 MB.
What bitrate should I use for YouTube 1080p?
YouTube recommends 8 Mbps for 1080p at 24–30 fps and 12 Mbps for 1080p at 48–60 fps (SDR uploads). Going higher rarely helps because YouTube re-encodes everything you upload; going much lower will show compression artifacts in fast motion.
What is a good bitrate for streaming on Twitch with OBS?
Twitch caps ingest around 6,000 kbps for most accounts. Common OBS settings are 6,000 kbps for 1080p60, or 4,500 kbps for 936p/900p60 if your upload bandwidth is limited. Your upload speed should be at least 1.4× the bitrate you set.
Why is my exported file bigger than the calculator predicted?
Most encoders use variable bitrate (VBR), so the average bitrate can overshoot your target on complex footage. Container overhead, embedded audio at a higher rate than expected, and two-pass vs single-pass encoding also shift the final size a few percent. Treat the calculation as a close estimate, not an exact promise.
Does resolution or frame rate change file size directly?
Not directly — file size depends only on bitrate × duration. But resolution and frame rate determine how much bitrate you need for acceptable quality: 4K60 footage needs roughly 4–6× the bitrate of 1080p30 to look equally clean.