TRANSPARENT ARITHMETIC
The method.
The limits.
A recording-storage calculator, not an encoder recommendation, disk monitor, or promise that a session will fit.
Measured recording mode
observed bytes/second = sample file bytes ÷ sample duration seconds
A 1 GiB recording lasting 10 minutes has an average of 6 GiB/hour. A similar two-hour session is estimated at 12 GiB before a planning buffer, or 15 GiB with a 25% buffer. Audio and container size are already in the sampled file; no separate audio estimate is added in this mode.
Known bitrate mode
bytes/second = (video Mbps × 1,000,000 + audio kbps × 1,000 × audio tracks) ÷ 8
At 8 Mbps with no audio, one hour is 3.6 GB before container overhead. One audio track at 192 kbps adds 0.0864 GB/hour. Use an observed average for VBR if you have one, or choose measured-recording mode for quality-based recording. A target bitrate is not a guarantee about the actual file.
Disk reserve and planning buffer
usable bytes = max(0, free bytes − reserve bytes)
planning rate = observed or entered rate × (1 + buffer% ÷ 100)
session budget = planning rate × session duration
time to reserve = usable bytes ÷ planning rate
A 50 GB free-space entry with a 10 GB reserve leaves 40 GB usable. At 8 Mbps and a 25% buffer, budget 4.5 GB/hour: eight complete one-hour sessions fit; about 8 h 53 min remain above the reserve. Displayed time is rounded down to whole minutes. Full-session counts use unrounded arithmetic, with a tiny floating-point tolerance at exact boundaries.
The buffer is an extra planning allowance, not an observed maximum. The example's 25% is not a tested safety recommendation. A reserve larger than current free space gives zero usable space. Space consumed by other apps, drive throughput, filesystem limits and failed recordings are not modeled.
Units and input limits
MB, GB and TB are decimal byte units; MiB, GiB and TiB are binary. Mbps and kbps are decimal bit rates. Prefer the exact byte count when converting a recorded file's size. Accepted input uses digits with one decimal point or comma, no grouping separators or exponent notation.
- Sample duration: 0.01–1,440 minutes. Sample size must be positive.
- Planned duration: 0.01–1,000 hours; buffer: 0–300%.
- Video: 0.001–100,000 Mbps; audio: 0–10,000 kbps per track; 0–32 whole-number tracks.
- Disk values: nonnegative, no more than 1 PB each. Session estimates over 1 PB are rejected.
- Numeric strings: at most 32 characters; no files or logs are accepted or interpreted.
Why there are no quality presets
A CQP/CRF/ICQ number does not specify a fixed file size. A scene's detail and motion can change the average rate; a short sample of an idle screen may understate gameplay. This tool does not use a proprietary benchmark database or claim a compression ratio for a codec.
OBS's official recording guide explains its quality-based settings. OBS's community bitrate example describes the bitrate-to-size arithmetic and audio contribution. These sources explain the inputs; they are not endorsements of this independent tool.
Scope and ownership
This version contains one calculator, helpful explanations and no ads. The original implementation and hand-drawn SVG icon use the MIT license. It is not affiliated with OBS, game publishers, recorder vendors or hosting providers. Site operator/contact details belong in the privacy disclosure before publication.