Video File Size Calculator

How Video File Size Is Calculated

Bitrate measures how much data a video stream uses per second. Multiplying bitrate by the total duration in seconds gives the total data in megabits, and dividing by 8 converts that to megabytes — the standard unit file sizes are reported in.

$$\text{Size (MB)} = \frac{\text{Bitrate} \times \text{Duration} \times 60}{8}$$

Worked Example

A 10 Mbps video that runs for 10 minutes (600 seconds): 10 times 600 equals 6,000 megabits, divided by 8 equals 750 megabytes. A higher bitrate of 50 Mbps (common for 4K footage) over the same 10 minutes would produce 50 times 600 divided by 8, or 3,750 megabytes — about 3.66 gigabytes.

Why Bitrate Varies So Much Between Videos

Resolution, frame rate, and codec efficiency all drive bitrate up or down independently of duration. A 4K video needs a much higher bitrate than 1080p to look equally sharp, since it has roughly four times the pixels to encode each frame; a more efficient codec (like H.265/HEVC compared to older H.264) can deliver similar visual quality at a meaningfully lower bitrate, which is why the same footage can produce very different file sizes depending on export settings.

A Brief History of Video Codecs

Digital video compression standardization began in earnest with the Moving Picture Experts Group, which released MPEG-1 in 1993 (the format behind Video CD) and MPEG-2 in 1995, the codec that made DVD and digital broadcast television practical by compressing video enough to fit the storage and bandwidth actually available at the time. Each successive standard chased the same goal: deliver acceptable quality at a lower bitrate than the one before it, since bitrate translates directly into file size and required bandwidth.

H.264 (also called AVC), standardized in 2003, roughly halved the bitrate needed for equivalent quality compared to MPEG-2 and became the codec behind most streaming video and smartphone recording for over a decade. H.265 (HEVC), finalized in 2013, pushed that efficiency further still, which is why two videos with identical resolution and visual quality can have very different bitrates and file sizes depending purely on which codec encoded them, the same tradeoff this calculator's bitrate field represents directly.

Common Video File Size Mistakes

Confusing megabits and megabytes is the most common error in this exact calculation — bitrate is almost always specified in megabits per second (Mbps), but file size is reported in megabytes (MB), and the two differ by a factor of 8. Skipping the division by 8 overstates the estimated file size eightfold.

Forgetting to convert duration from minutes to seconds before multiplying by a per-second bitrate is another — the formula above already includes the times-60 conversion, but a manual calculation done by hand often misses it.

Video File Terms You Should Know

Bitrate — the amount of data used per second of video, usually measured in megabits per second (Mbps); higher bitrate generally means higher quality and a larger file.

CBR vs. VBR — Constant Bitrate encodes every second at the same bitrate; Variable Bitrate adjusts bitrate scene by scene, using more data for complex motion and less for static scenes, often producing a smaller file at similar quality.

Codec — the compression algorithm (like H.264 or H.265) used to encode video; more efficient codecs achieve similar quality at a lower bitrate.