Media Bitrate & File Size Calculator
File size, bitrate and duration are locked together: any two determine the third. The one place people go wrong is the factor of eight — bitrate is quoted in bits per second while file size is measured in bytes, so a 10 Mbps stream produces 1.25 MB each second, not 10.
How to use this tool
- Choose whether you want the file size, the bitrate needed for a target size, or how long your storage will last.
- Enter the video bitrate and its unit. Add the audio bitrate too — it is easy to overlook and adds up over a long recording.
- Enter the duration in hours and minutes, or the available size, depending on the mode.
- The result appears immediately, with the same figure expressed in several units beneath it.
- Treat every figure as an estimate: variable-bitrate encoding means the real size will vary around it.
The formula
File size follows directly from bitrate and duration. The one place people go wrong is the factor of eight: bitrate is quoted in bits per second while file size is measured in bytes, so a 10 Mbps stream produces 1.25 MB of data each second, not 10.
bits = (video_bitrate + audio_bitrate) × seconds
bytes = bits ÷ 8
required_bitrate = (target_bytes × 8) ÷ seconds- bitrate
- Bits per second; kbps, Mbps and Gbps are its multiples
- ÷ 8
- Bits to bytes — eight bits make one byte
- audio_bitrate
- Often forgotten, but adds up over a long recording
These figures assume constant bitrate. Variable-bitrate encoding, which most modern codecs use by default, allocates more data to complex scenes and less to simple ones, so the real file size will vary around this estimate rather than match it exactly.
Worked examples
An hour of 1080p video
- Given
- 8 Mbps video plus 192 kbps audio for 1 hour
- Result
- 3.69 GB
Combined bitrate is 8.192 Mbps. Over 3600 seconds that is 29,491 megabits, and dividing by 8 gives 3,686 megabytes.
Fitting a talk onto a 700 MB disc
- Given
- 700 MB target for a 45-minute recording
- Result
- 2.07 Mbps
700 MB is 5,600 megabits. Divided by 2,700 seconds that allows about 2.07 Mbps for video and audio combined.
How long a memory card lasts
- Given
- 128 GB card at 100 Mbps
- Result
- About 2 hours 50 minutes
128 GB is 1,024 gigabits. At 100 Mbps that is 10,240 seconds. High bitrate camera formats fill storage far faster than people expect.
Frequently asked questions
Almost certainly variable-bitrate encoding. Most modern codecs spend more data on complex scenes and less on simple ones, so a video with long static shots comes in well under the constant-bitrate estimate. Treat the figure as an upper bound for VBR content.
The capitalisation is the whole difference and it matters by a factor of eight. Lowercase b is bits; uppercase B is bytes. A 100 Mbps connection transfers about 12.5 MB per second. Internet providers quote bits, which makes their numbers look larger.
As a rough guide, 3 to 6 Mbps for 1080p at 30fps, 6 to 9 for 1080p at 60fps, and 15 to 25 for 4K. Newer codecs such as AV1 and HEVC achieve the same quality at noticeably lower rates. Platform limits often matter more than what your encoder can produce.
Bitrate, past a point. A 4K stream starved of bitrate looks worse than a well-encoded 1080p one, because the encoder has to discard detail to fit. Higher resolution only helps if there is enough data budget to carry it.
They count differently. Manufacturers use decimal units where a gigabyte is 1,000,000,000 bytes; many operating systems display binary units where a gibibyte is 1,073,741,824. A 1 TB drive therefore shows as about 931 GiB. This calculator uses decimal units, matching how storage is sold.
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