How to Calculate Bitrate

Updated

Work out a file's bitrate from its size and running time, size a file from its bitrate, and pick a live-stream bitrate your connection and the platform will both accept.

Quick Bitrate Formula Reference

Basic Bitrate Formula

Bitrate = File Size / Duration

Where file size is in bits and duration is in seconds

Streaming Rule of Thumb

Video + Audio ≤ 80% of Upload Speed

Leaves headroom for dips in your connection, then stay under the platform's own ceiling

Understanding Bitrate

What is Bitrate?

Bitrate is how many bits a stream or file uses per second of running time. Video rates are quoted in kilobits or megabits per second: 1 Mbps = 1,000 Kbps = 1,000,000 bits per second. For a given codec and resolution, bitrate sets both the picture quality and the file size.

Watch the case of the B. Network speeds and bitrates are in bits (Mbps); drive and file-copy speeds are usually in bytes (MB/s). One byte is 8 bits, so 1 MB/s = 8 Mbps.

Higher Bitrate

  • • Better quality, up to the point where the codec has nothing left to gain
  • • Larger file sizes
  • • More bandwidth required

Lower Bitrate

  • • Smaller file sizes
  • • Potential quality loss
  • • Less bandwidth required

How to Calculate Bitrate

Method 1: Calculate from File Size

Formula:

Bitrate (bps) = File Size (bytes) × 8 ÷ Duration (seconds)

Multiply by 8 to turn bytes into bits. The answer is the file's overall bitrate: video, audio and container together.

Example:

A 2 GB video file that is 30 minutes long:

File Size: 2 GB = 2,000,000,000 bytes

Duration: 30 minutes = 1,800 seconds

Bitrate = (2,000,000,000 × 8) ÷ 1,800 = 8,888,889 bps

Result: 8.89 Mbps

GB here is decimal (1,000,000,000 bytes), the unit drive makers and macOS use. Windows labels binary gibibytes as "GB": a file it shows as 2 GB is 2 × 1,073,741,824 bytes, which works out to 9.54 Mbps. The two units differ by 7.4%. The TB vs TiB guide shows which tools count which way.

Run it backwards to size a file: File Size (GB) = Bitrate (Mbps) × Duration (seconds) ÷ 8,000. 8.89 Mbps for 1,800 seconds is 8.89 × 1,800 ÷ 8,000 = 2.0 GB. The free bitrate calculator does this in your browser.

Method 2: Calculate for Streaming

Formula:

Video Bitrate = (Upload Speed × 0.8) − Audio Bitrate

Then use the lower of that figure and the platform's recommendation. The 80% is a rule of thumb for headroom, not a platform rule: Twitch and YouTube both say a stable stream matters more than a high bitrate.

Example:

A speed test shows 10 Mbps upload, and you want to stream 1080p60 with 160 Kbps audio:

Budget: 10 × 0.8 = 8 Mbps

Video: 8 − 0.16 = 7.84 Mbps (7,840 Kbps)

Twitch recommends 6,000 Kbps for 1080p60, so set 6,000 Kbps

YouTube recommends 17,000 Kbps (minimum 6,000), so set about 7,800 Kbps

Result: 6,000 Kbps on Twitch; about 7,800 Kbps on YouTube

Method 3: Calculate for a Target File Size

Formula:

Video Bitrate (Mbps) = Size (GB) × 8,000 ÷ Duration (s) − Audio (Mbps)

For an upload limit, a disc or a delivery spec that caps file size. Aim slightly under, since the container adds a little on top.

Example:

A 45-minute episode has to fit in 4 GB, with 192 Kbps stereo audio:

Total: 4 × 8,000 ÷ 2,700 = 11.85 Mbps

Video: 11.85 − 0.192 = 11.66 Mbps

Result: encode the video at about 11.5 Mbps

Live-Stream Bitrates by Platform

Each platform's own H.264 recommendations, checked October 2026. All three ask for a keyframe every 2 seconds; Twitch also asks for constant bitrate (CBR).

Twitch

  • • 1080p 60fps: 6,000 Kbps
  • • 1080p 30fps: 4,500 Kbps
  • • 720p 60fps: 4,500 Kbps
  • • 720p 30fps: 3,000 Kbps
  • • Audio: AAC-LC, 96 Kbps recommended, 160 Kbps maximum
  • • Source: Twitch Broadcasting Guidelines

YouTube

  • • 1080p 60fps: 17,000 Kbps (minimum 6,000)
  • • 1080p 30fps: 14,000 Kbps (minimum 5,000)
  • • 720p 60fps: 8,000 Kbps (minimum 3,000)
  • • 720p 30fps: 8,000 Kbps (minimum 3,000)
  • • Audio: AAC or MP3, 128 Kbps stereo (384 Kbps for 5.1, AAC only)
  • • Source: YouTube Live encoder settings
  • • For uploads rather than live streams, see the YouTube video specs

Facebook

  • • 1080p 60fps: 4,500–9,000 Kbps
  • • 1080p 30fps: 3,000–6,000 Kbps
  • • 720p 60fps: 2,250–6,000 Kbps
  • • 720p 30fps: 1,500–4,000 Kbps
  • • Audio: AAC-LC, 44.1 or 48 kHz stereo, 128 Kbps (256 Kbps maximum)
  • • Source: Meta Live Video API

Common Bitrate Calculation Mistakes

❌ Avoid These Mistakes

  • • Streaming at 100% of your measured upload speed
  • • Reading MB/s as Mbps (they differ by a factor of 8)
  • • Mixing decimal GB and binary GiB (7.4% apart)
  • • Leaving audio out of the total
  • • Dividing by minutes when the formula wants seconds

✅ Best Practices

  • • Keep video plus audio within about 80% of upload speed
  • • Multiply bytes by 8 to get bits
  • • Use the platform's figure when it is lower than your budget
  • • Run a test stream before the real one
  • • Watch the encoder's dropped-frame count while live

Tools for Bitrate Calculation

CineMath Calculator

Data & Storage in CineMath solves for file size, record time or the bitrate that hits a target size (Method 3, with audio taken out). Rates can be typed in or taken from generic codec presets; camera presets with each maker's published rates come with Pro.

See Data & Storage

Upload Time

For a finished file rather than a live stream: Upload Time works out how long it takes to send at your connection speed, with a best-to-worst-case range.

See Upload Time