Video Bitrate Calculator
Calculate video file size from bitrate and duration, or the bitrate needed to hit a target file size. Includes the audio track and shows the full formula and steps.
Updated 2026-06-14 · Free · No sign-up · Runs privately in your browser
Show the formula & steps
How the Video Bitrate Calculator Works
This calculator connects the three quantities that govern any video file: bitrate, duration, and file size. Choose whether to solve for file size (given a bitrate) or for the bitrate (given a target size), enter the duration and the audio bitrate, and it returns the result with a full breakdown.
The Formula
Bitrate is data per second, so file size is simply bitrate multiplied by time:
Total bitrate (Mbps) = video bitrate + audio bitrate File size (megabits) = total bitrate × duration (seconds) File size (megabytes) = megabits ÷ 8
To go the other way and find the bitrate for a target size, rearrange:
Total bitrate (Mbps) = (target MB × 8) ÷ duration (seconds)
There are 8 bits in a byte, which is why the divide-by-8 step appears.
Worked Example
Encode a 60-minute video at 8 Mbps video plus 128 kbps audio:
- Total bitrate = 8 + 0.128 = 8.128 Mbps
- Duration = 60 min = 3,600 s
- Megabits = 8.128 × 3,600 = 29,260.8 Mb
- File size = 29,260.8 ÷ 8 = 3,657.6 MB ≈ 3.66 GB
Going the other way, to fit a 60-minute video into 700 MB:
- 700 MB × 8 = 5,600 megabits
- Total bitrate = 5,600 ÷ 3,600 = 1.556 Mbps
- Video bitrate = 1.556 − 0.128 = 1.428 Mbps
| Scenario | Total bitrate | Result |
|---|---|---|
| 8 Mbps, 60 min | 8.128 Mbps | 3.66 GB |
| Fit 700 MB, 60 min | 1.556 Mbps | 1.428 Mbps video |
Choosing a Bitrate
Higher bitrate means better quality and a larger file. Typical targets:
- 480p: 1–2 Mbps
- 720p: 2.5–5 Mbps
- 1080p: 8–12 Mbps
- 4K: 35–45 Mbps
Why It Matters
Estimating file size before you encode saves time when you need a clip to fit an upload limit, a streaming cap, or a storage budget. Because the math assumes a constant average bitrate, the result is a close planning estimate; variable-bitrate encodes will land within a few percent of it after accounting for container overhead.
Frequently asked questions
How do you calculate video file size from bitrate?+
Multiply the total bitrate in megabits per second by the duration in seconds to get the size in megabits, then divide by 8 to convert to megabytes. For example, 8 Mbps for 60 minutes is 8 x 3600 = 28,800 megabits, which is 28,800 / 8 = 3,600 MB before adding the audio track.
How do I find the bitrate for a target file size?+
Convert the target size to megabits by multiplying megabytes by 8, then divide by the duration in seconds to get the total bitrate. Subtract the audio bitrate to find how much is left for video. This is exactly how you size a video to fit a disc, an upload limit, or a streaming cap.
Should I include the audio bitrate?+
Yes. The file holds both the video and audio streams, so the total bitrate is video plus audio. A 128 kbps audio track adds about 0.96 MB per minute. This calculator adds the audio bitrate automatically and shows the combined total so the file-size estimate is realistic.
Why is my actual file slightly different from the estimate?+
The formula assumes a constant average bitrate and ignores container overhead, variable-bitrate fluctuations, and metadata. Real files using variable bitrate (VBR) encoding will hover around the average, so the estimate is accurate to within a few percent for planning purposes rather than to the exact byte.
What bitrate should I use for 1080p video?+
A common range for 1080p at 30 fps is roughly 8 to 12 Mbps for high quality, dropping to 4 to 6 Mbps for streaming. 4K typically needs 35 to 45 Mbps. Higher motion and frame rates need more. Use this calculator to see how a chosen bitrate translates into final file size before you encode.