Know the size before you press record.

What it computes

One line of arithmetic: bytes = (video bit/s + audio bit/s) × seconds ÷ 8. Type the length of one recording and the average bitrate you expect; the page shows the size of one recording and of the whole batch, in both unit families, and checks it against the space you have.

• Average bitrate. A constant-bitrate encoder (CBR) holds the number you typed. Variable-bitrate modes (VBR) and the quality-based modes behind recording presets (CRF, CQP, ICQ) spend more bits on busy frames and fewer on quiet ones, so the real file lands above or below the estimate. For those, type the measured average of a past recording rather than a target.
• Audio. Added on top of the video. Recordings often carry one or two tracks; the Broker’s voice is part of Desktop Audio, not an extra track, so there is nothing to add for him.
• Container allowance. MP4 and MKV wrap the streams with index and timing data, usually a fraction of a percent. The developer’s measured copy came out 0.34% above bitrate × time (second example below). 0 keeps the plain arithmetic.
• Fits in. With a storage budget filled in, the page says whether the batch fits, what is left, and how many recordings of this size would fit.

Worked examples

The three example buttons above fill the form with these figures. They are examples of the arithmetic, not recommended settings.

Where the figures come from: 6,000 kbps is the service-ceiling example the OBS Studio Overview Guide gives for Twitch, and 160 kbps is the audio figure it suggests for streaming; neither is a recording recommendation. The Dead Cells numbers were measured with ffprobe on the copy of the public upload in the site’s evidence folder (1920 × 804, 60 fps, 640.2 s, 258,112,903 bytes). It is YouTube’s re-encode, not the original OBS recording, so it checks the arithmetic and says nothing about what OBS wrote to disk. The third row is invented to show a batch against a budget.

Which bitrate to type

There is no universal right bitrate. It depends on resolution, frame rate, encoder, the game’s motion and how much quality loss you accept, and this page does not recommend one. Three ways to get a number that is yours:

1. 01Read it from a past recording

   In Explorer, right-click the file → Properties → Details: Windows lists a total bitrate in kbps (video and audio together). Type it as the video bitrate with audio at 0. Or divide the file’s size in bits by its length in seconds.

2. 02Read it from OBS

   Settings → Output. The OBS Studio Overview Guide describes recording by preset (Same as stream, High Quality, Indistinguishable Quality, Lossless); those presets are quality-based and show no bitrate, and only Same as stream uses the stream’s Video Bitrate field. The Standard Recording Output Guide says a separate recording encoder lets you set “bitrate, quality presets and keyframe interval”, so in Advanced output a bitrate-based rate control shows its number in the encoder settings.

3. 03Record one minute and measure

   The quickest truth: record 60 seconds of the game at your settings, read the file size, and the average bitrate is size in bits ÷ 60.

For context only: the Overview Guide says the stream video bitrate “changes according to your upload speed and the limitations of the service you use (for example, 6000kbps max for Twitch.tv)”, and suggests “around 160kbps” of audio for streaming. Recording to disk has no upload limit, so many people record at a higher bitrate than they stream; how much higher is their choice, and this page only tells them what it costs in space.

GB or GiB?

Two unit families share the same letters. Decimal units count in thousands: 1 GB = 1,000,000,000 bytes; drive labels, encoders and this page’s “GB” use them. Binary units count in 1,024s: 1 GiB = 1,073,741,824 bytes, about 7.4% bigger. Windows Explorer measures in binary units but labels them “MB” and “GB”, which is why a drive sold as 500 GB shows about 465 GB there and a 2.77 GB file shows as 2.58 GB. The page prints both so its numbers agree with wherever you look.

MB / MiB

1 MB = 1,000,000 bytes · 1 MiB = 1,048,576 bytes

GB / GiB

1 GB = 1,000,000,000 bytes · 1 GiB = 1,073,741,824 bytes

TB / TiB

1 TB = 1,000,000,000,000 bytes · 1 TiB = 1,099,511,627,776 bytes

Bitrates

Always decimal and in bits: 1 kbps = 1,000 bit/s, 1 Mbps = 1,000,000 bit/s; 8 bits make a byte

What the estimate assumes

• A constant average. The bitrate is applied to every second. Replay buffers, scene changes, pauses and encoder look-ahead are not modelled.
• Bits, not bytes. The bitrate fields are in kilobits or megabits per second, as encoders report them. A “6 MB/s” figure from somewhere else would be 48 Mbps.
• One container figure. The allowance is a flat percentage; real overhead varies with the container, the keyframe interval and the number of tracks.
• Input ranges. The page refuses negative numbers, zero duration, zero video bitrate, non-numeric text, more than 100 hours per recording, more than 2,000 Mbps, more than 20,000 kbps of audio, more than 10,000 recordings and allowances over 100%, each with a message naming the field.
• Rounding. Results are rounded for display; the arithmetic uses the exact byte count, shown in the copyable block.

Limits

• An estimate: it applies one average bitrate to the whole recording. Variable-bitrate and quality-based encoder modes produce files above or below it; the file on disk is the only exact number.
• No bitrate recommendation: the page explains how to read your own average from OBS or a past recording and quotes OBS’s documentation for context only. It does not state platform rules.
• The container allowance is a flat percentage you choose; real overhead depends on the container, keyframe interval and tracks.
• Founder Alpha is early-access software; the commentary can be wrong, repeated or badly timed, and it is sold to customers in the United States only.