Running out of card space halfway through a recording is a painful lesson, and exporting a video only to find a 40 gigabyte file is another. Both problems come from the same missing number: how big will the video be. This estimator answers it before you press record or export. Enter the video bitrate, the audio bitrate, and the duration, and it estimates the file size, the size per hour, and how many hours fit on your card or drive, using simple bitrate maths and nothing else.
The maths is bitrate times time. Video bitrate plus audio bitrate gives total kilobits per second. Multiply by seconds to get kilobits, divide by eight to get kilobytes, and scale to gigabytes. A 10 megabit per second video stream with 192 kilobit audio runs at 10,192 kilobits per second. Over thirty minutes, that is about 2.29 gigabytes. Double the duration and you double the size; double the bitrate and you also double the size. Nothing else in the estimate matters as much as those two numbers.
Here is a worked example for a creator planning a shoot. You record 60 minutes at 25 megabits per second video and 256 kilobits audio, which totals 25,256 kilobits per second. Over one hour that is about 11.36 gigabytes. On a 64 gigabyte card, you fit about 5.6 hours at that setting, before formatting overhead. Drop the video bitrate to 12 megabits per second and the same hour shrinks to about 5.5 gigabytes, fitting roughly 11.6 hours. Bitrate choice is therefore a storage choice, not just a quality choice.
Bitrate and quality trade off in a curve, not a straight line. Raising bitrate improves quality sharply at first, then yields smaller and smaller gains, while file size keeps growing at the same rate. A simple talking head video needs far less bitrate than fast sports footage, because still scenes compress well and busy motion does not. That is why two videos at the same bitrate can look different: the bitrate budget stretches further on calm scenes than on chaotic ones.
Variable bitrate adds a wrinkle worth knowing. Constant bitrate spends the same data every second, so the estimate is nearly exact. Variable bitrate spends less on still scenes and more on busy ones, so a quiet interview comes out smaller than the estimate, while an action scene comes out close to it or slightly larger. Treat the result as a planning ceiling for variable bitrate footage: if the estimate fits your card, the real file usually fits too, with room to spare.
Audio bitrate is small but not invisible. At 192 kilobits per second, audio adds about 86 megabytes per hour, which is minor next to gigabytes of video. At uncompressed or very high audio rates, the share grows, and for audio led recordings like podcasts with video, it deserves a real entry rather than a guess. Always enter the audio rate your export or camera actually uses, because a default of zero understates every estimate, even if only slightly.
Use the estimate at three moments: before recording, before exporting, and before buying storage. Before recording, it tells you whether the card survives the shoot. Before exporting, it tells you whether the file fits an upload limit or a sharing service. Before buying storage, it turns a vague feeling into hours of footage per card, so you buy the size you need instead of the biggest card in the shop. This tool only estimates from numbers you enter: it never uploads, converts, or processes any video file. Keep the three input numbers written on the shoot plan, and every future estimate takes seconds instead of starting from scratch.