OBS File Size Calculator: Estimate Recording Size

This calculator estimates the file size of an OBS (Open Broadcaster Software) recording or stream based on bitrate, duration, and resolution. Enter your video bitrate, audio bitrate, and recording length to get the approximate file size in megabytes and gigabytes.

Formula

The file size is calculated by converting bitrates to bytes per second, then multiplying by the duration in seconds. The formula is:

File Size (MB) = ((Video Bitrate (Mbps) × 1000 / 8) + (Audio Bitrate (Kbps) / 8)) × Duration (seconds) / 1000

Where:

• Video Bitrate – the bitrate set in OBS for the video stream, in megabits per second (Mbps).
• Audio Bitrate – the bitrate set for the audio track, in kilobits per second (Kbps).
• Duration – the total recording time in minutes (converted to seconds by multiplying by 60).
• File Size – the resulting size in megabytes (MB) or gigabytes (GB).

Note: This formula uses decimal (1000-based) units, which is how storage devices and OBS typically report file sizes. If you see a slightly different size on your computer (using 1024-based MiB/GiB), that explains the difference.

Worked Example

Using the default values: video bitrate = 8 Mbps, audio bitrate = 160 Kbps, duration = 60 minutes.

1. Convert video bitrate to bytes per second: 8 Mbps × 1000 / 8 = 1000 KB/s (kilobytes per second).
2. Convert audio bitrate to bytes per second: 160 Kbps / 8 = 20 KB/s.
3. Total bytes per second: 1000 + 20 = 1020 KB/s.
4. Convert duration to seconds: 60 minutes × 60 = 3600 seconds.
5. Total bytes: 1020 KB/s × 3600 s = 3,672,000 KB.
6. Convert to MB: 3,672,000 KB / 1000 = 3672 MB.
7. Convert to GB: 3672 MB / 1000 = 3.672 GB.

The calculator shows 3672.00 MB and 3.67 GB, matching the manual calculation.

How OBS Bitrate Settings Affect File Size

OBS lets you choose between CBR (Constant Bitrate) and VBR (Variable Bitrate) for recording. CBR keeps the bitrate at the set value, so file size is predictable using the formula above. VBR adjusts bitrate based on scene complexity, which can reduce file size for static scenes but may increase it for fast motion. For streaming, CBR is typically required by platforms like Twitch or YouTube, but for local recordings you might use VBR or CRF (Constant Rate Factor) in x264. With CRF, the bitrate varies, so this calculator gives an average estimate—actual size can differ.

Choosing the Right Bitrate for Your Recording

Selecting a bitrate depends on resolution, frame rate, and content type. Here are general guidelines:

• 720p at 30 fps – 4.5 to 6 Mbps for streaming, 6 to 8 Mbps for recording.
• 1080p at 30 fps – 6 to 8 Mbps for streaming, 8 to 12 Mbps for recording.
• 1080p at 60 fps – 9 to 12 Mbps for streaming, 12 to 18 Mbps for recording.
• 1440p at 60 fps – 16 to 20 Mbps for streaming, 20 to 30 Mbps for recording.
• 4K at 60 fps – 35 to 45 Mbps for streaming, 45 to 60 Mbps for recording.

Higher bitrates produce better quality but larger files. For local recordings, use a higher bitrate since storage is usually cheaper than re-recording. For streaming, stay within the platform’s recommended limits to avoid buffering.

Common Mistakes and Misconceptions

One common mistake is mixing up megabits (Mb) and megabytes (MB). A bitrate of 8 Mbps equals 1 MB/s (8/8 = 1), but many people incorrectly assume 8 Mbps = 8 MB/s. Another error is using 1024 instead of 1000 in calculations—OBS and most operating systems report file sizes in decimal units (1 GB = 1000 MB), but some tools use binary (1 GiB = 1024 MiB), leading to a ~5% difference. Also, this calculator ignores container overhead (e.g., MP4, MKV) and keyframe intervals, which add a tiny amount (usually less than 1%). For variable bitrate recordings, the actual size can be 10–30% different from the estimate.

Practical Tips for Managing Recording Size

If you need to reduce file size without sacrificing quality, consider:

• Use a lower resolution or frame rate if the content doesn’t require high motion.
• Switch to H.265/HEVC encoding if your hardware supports it—it can halve file size at the same quality.
• Use a variable bitrate with a higher CRF value (e.g., 23 instead of 18) for local recordings.
• Trim recordings after capturing to remove unused segments.
• Store recordings on an external drive or use cloud storage to avoid filling your main disk.

Limitations of the Calculator

This calculator provides an estimate based on average bitrate. Actual file size depends on the encoder, preset, and content complexity. For example, a talking-head video with a static background will compress much better than a fast-paced game with particle effects. Also, OBS adds a small overhead for the container and audio track synchronization, typically under 1% of total size. The estimate is most accurate for CBR recordings with a fixed bitrate.

Frequently Asked Questions

How do I find my current bitrate in OBS?

In OBS, go to Settings > Output. Under the Streaming or Recording tab, you’ll see a Bitrate field. If you’re using a preset like ‘High Quality, Medium File Size’, the bitrate is set automatically—you can check the log file (View > Logs) or use a tool like Task Manager to see the actual bitrate during recording.

Does the file size calculator work for streaming?

Yes, but for streaming the duration is the length of the stream. The calculation is the same; however, streaming platforms often re-encode your video, so the file size you upload after downloading from the platform may differ.

Why does my actual file size differ from the estimate?

Most likely because you’re using variable bitrate (VBR) or a CRF setting, which changes bitrate based on scene complexity. Also, check if you’re comparing decimal GB (1000 MB) vs binary GiB (1024 MiB). The difference is about 5%.

Can I reduce file size without losing quality?

Yes, by using a more efficient encoder like H.265/HEVC or AV1, or by increasing the CRF value slightly (e.g., from 18 to 23) for local recordings. However, there’s a trade-off: higher CRF reduces quality, especially in high-motion scenes.

How much storage do I need for a 2-hour recording?

Using the default settings (8 Mbps video, 160 Kbps audio), a 2-hour recording would be about 7.3 GB. For 1080p at 60 fps with 12 Mbps, it would be about 10.9 GB. Always plan for the maximum bitrate you might use.

Does resolution affect file size separately from bitrate?

No, resolution only affects file size indirectly because higher resolutions typically require higher bitrates to maintain quality. If you keep the same bitrate, a 4K video will be the same size as a 720p video, but the 4K will look worse due to compression.

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in b | Video bitrate | Mbps | 8 | 0
in a | Audio bitrate | Kbps | 160 | 0
in t | Duration | minutes | 60 | 0
out size_mb | File size | MB | (b * 1000 / 8 + a / 8) * t * 60 / 1000 | 2
out size_gb | File size | GB | (b * 1000 / 8 + a / 8) * t * 60 / 1000000 | 2