Video File Size Calculator

File size for a finished video is pure unit arithmetic: add the video and audio bitrates, multiply by the running time in seconds, and divide by 8 because storage is counted in bytes while bitrate is quoted in bits. A ten-minute program at 8 Mbps video plus 256 kbps audio carries 8.256 Mbps over 600 seconds, or 4,953.6 megabits, which is 619 MB. The audio term matters more than people expect on long-form content: 256 kbps of AAC adds about 115 MB per hour, and uncompressed 48 kHz 16-bit stereo PCM at 1,536 kbps adds roughly 691 MB per hour. Container overhead for MP4 or MKV headers, indexes, and timecode is small, generally under one to two percent of the payload. Two caveats regularly break naive estimates. The first is prefix ambiguity: operating systems and drive manufacturers disagree on whether a megabyte is 1,000,000 or 1,048,576 bytes, a gap that grows to about 7 percent at the gigabyte scale and about 10 percent at the terabyte scale, so a file reported as 1.00 GB by a camera may show as 0.93 GB in a file browser. The second is rate control. This arithmetic assumes an average bitrate is known in advance, which is true for constant bitrate and for capped average-bitrate VBR, but not for constant-quality modes such as x264 or x265 CRF, where the encoder holds quality fixed and the resulting bitrate is discovered only after the encode finishes.

The units in this calculation predate digital video by decades. Claude Shannon credited John Tukey with coining the word bit in his 1948 paper A Mathematical Theory of Communication, and Werner Buchholz named the byte at IBM in 1956 during the design of the Stretch computer, with eight bits becoming the settled width through the System/360 in 1964. The habit of quoting transmission in bits per second and storage in bytes comes directly from that split between communication engineering and computer memory, and it is why the factor of eight appears in every file-size estimate. Confusion over decimal versus binary multiples was formally addressed in 1998, when the International Electrotechnical Commission published IEC 60027-2 defining kibibyte, mebibyte, and gibibyte for the powers of 1,024. Practical size budgeting became routine in the tapeless transition. DV, standardized in 1995, locked video at 25 Mbps, so an hour of footage was always about 13 GB and a 60-minute MiniDV cassette had a fixed, predictable payload. The MP4 container that dominates delivery today was standardized as ISO/IEC 14496-14 in 2003, built on the ISO base media file format derived from Apple QuickTime, whose specification Apple contributed to MPEG in 1998. Advanced Audio Coding, defined in MPEG-2 Part 7 in 1997, replaced MP3 as the default soundtrack codec and set the 128 to 320 kbps range still used for the audio term.