How to Calculate Video Bitrate and File Size
Video bitrate measures the amount of data processed per second of video, usually expressed in megabits per second (Mbps) or kilobits per second (kbps). Determining your target bitrate allows you to balance visual quality against platform upload limits, storage constraints, and streaming bandwidth caps.
The Video Bitrate Formula
File Size (MB) = [(Video Bitrate + Audio Bitrate in kbps) × Duration in Seconds] ÷ (8 × 1024)
Tip: 1 Byte = 8 bits. Divide bits by 8, then divide by 1,024 to convert Kilobytes (KB) to Megabytes (MB).
Recommended Bitrate Settings Reference Table
Standard export guidelines for H.264 / MP4 uploads across YouTube, Vimeo, and streaming services:
| Resolution | Framerate | Standard Video Bitrate (SDR) | Recommended Audio Bitrate |
|---|---|---|---|
| 720p HD (1280×720) | 24 / 30 fps | 5,000 kbps (5 Mbps) | 128–192 kbps (AAC) |
| 1080p Full HD (1920×1080) | 24 / 30 fps | 8,000 kbps (8 Mbps) | 192–256 kbps (AAC) |
| 1080p High Framerate (1920×1080) | 60 fps | 12,000–15,000 kbps (12–15 Mbps) | 256–320 kbps (AAC) |
| 1440p 2K (2560×1440) | 60 fps | 24,000 kbps (24 Mbps) | 320 kbps (AAC) |
| 4K Ultra HD (3840×2160) | 24 / 30 fps | 35,000–45,000 kbps (35–45 Mbps) | 320 kbps (AAC) |
| 4K High Framerate (3840×2160) | 60 fps | 53,000–68,000 kbps (53–68 Mbps) | 320 kbps (AAC) |
CBR vs. VBR: Which Should You Choose?
- Constant Bitrate (CBR): Allocates the exact same data rate to every second regardless of scene complexity. Best for live streaming (Twitch, YouTube Live, OBS) where network buffers require predictable bandwidth.
- Variable Bitrate (VBR 1-Pass / 2-Pass): Dynamically raises bitrate during complex motion and lowers it during static scenes. Best for video on demand (VOD), editing exports, and reducing overall file size without sacrificing clarity.
Frequently Asked Questions
What is my video's bitrate?
Your video's bitrate is the total data throughput needed to play 1 second of content. You can calculate it by dividing your file size (in bits) by the video duration (in seconds).
Why is my exported file size larger than expected?
High audio sample rates, uncompressed audio channels (PCM instead of AAC), and complex multi-pass VBR render settings can significantly increase the total byte count.
What bitrate should I use for OBS live streaming?
For 1080p 60fps on Twitch, set your video bitrate to 6,000 kbps (CBR) and audio to 160 kbps. For YouTube Live at 1080p 60fps, settings between 6,000 and 9,000 kbps provide high stability.
How is video file size calculated from bitrate?
File size is calculated by multiplying total bitrate (video bitrate plus audio bitrate) by duration in seconds, then dividing by 8 to convert bits into bytes: File Size (MB) = [(Video Bitrate kbps + Audio Bitrate kbps) × Duration (seconds)] / (8 × 1024).
What is a good bitrate for 1080p 60fps video?
For standard SDR 1080p at 60 fps, YouTube and Vimeo recommend a video bitrate between 12 Mbps and 15 Mbps (12,000–15,000 kbps) using H.264 / AVC encoding. For live streaming on Twitch or YouTube Live, 6,000 to 8,000 kbps is the standard range.
What bitrate should I use for 4K video exports?
For 4K UHD (3840×2160) at 24/30 fps in H.264, use 35 to 45 Mbps. For 4K at 60 fps, use 53 to 68 Mbps. If encoding in H.265 (HEVC) or AV1, you can reduce these rates by 30% to 50% while preserving the same visual fidelity.
Does audio bitrate affect the total video file size?
Yes. Audio streams contribute directly to the total file size. For example, a 1-hour stereo track at 320 kbps AAC adds approximately 144 MB to the final export size.
Understanding Data Rate Dynamics
Bitrate defines how much digital information your player or browser must process every second of playback.
Think of bitrate like a hose. A wide hose (high bitrate) can carry a lot of water (visual detail) through it every second. A narrow hose (low bitrate) can only carry so much — and if you try to push more detail through it than it can handle, compression artifacts appear.
The texture in fine hair, smooth gradients in sunset skies, and crisp edges of on-screen text turn into blurry macroblocks when data is constrained.
Bitrate is measured in megabits, but storage space is measured in megabytes, and there are 8 bits in 1 byte.
A video encoded at 40 Mbps writes 5 MB per second to your hard disk. Keeping this 8:1 ratio in mind prevents costly storage miscalculations.
Resolution and Framerate Synergy: A 4K video contains four times the pixel information of a 1080p video at the same frame rate. Encoding 4K footage using 1080p bitrates forces the encoder to drop fidelity, creating noticeable compression banding in gradients and motion blur.
Two Ways to Use This Calculator
Solve for your unknown constraint depending on your production deliverable:
If an upload destination caps file size (such as Discord 25MB/50MB or an email server limit), enter duration and size cap to receive the exact target bitrate needed to never exceed the threshold.
If you have set bitrates in Premiere, Final Cut, DaVinci Resolve, or Handbrake, calculate how much disk space your finished render will consume before beginning long rendering sessions.
When estimating storage requirements quickly on set without a calculator: at 45 Mbps delivery bitrate, expect roughly 340 MB per minute of footage.
Bitrate and file size scale linearly: halving the bitrate halves the file size for an identical duration.
All calculations and conversions take place immediately inside your browser. No files, metadata, or metrics are uploaded or transmitted to any server.