Video File Size Calculator

Bits, bytes and the one formula that matters

A video file is a long run of bits. The bitrate says how many bits are spent each second, and the length of the clip says how many seconds there are. Multiply the two and you have the size in bits. Divide by 8 and you have bytes.

Size in megabytes = bitrate in Mbps x seconds / 8

That covers the picture. A 10 minute clip at 8 Mbps is 8 x 600 = 4,800 megabits, and 4,800 / 8 = 600 megabytes. The sound is added the same way. Most uploads use 128 kbps for stereo audio, which is 0.128 Mbps, so 0.128 x 600 / 8 = 9.6 megabytes. The container then adds a small amount for indexes and headers. Allow 3 percent and the finished file sits at 627.9 MB.

Megabyte in this calculator means 1,000,000 bytes. Windows and some camera apps report size in mebibytes, which are 1,048,576 bytes. The same 627.9 MB file shows as 599 MiB there. Neither number is wrong. The unit is different, and that gap is about 4.8 percent on every file you check.

Bitrate decides almost everything

Resolution and frame rate only matter because they push the bitrate up. The platform publishes a target for each combination, and that target is what sets the size. The table below uses the recommended SDR upload bitrates published in YouTube's encoding settings guide.

The per hour column is bitrate x 3600 / 8, which works out to bitrate x 450 megabytes. An 8 Mbps file adds 3,600 MB for every hour, or 3.6 GB. A 45 Mbps file adds 20,250 MB, or 20.3 GB. Once you know that one factor, you can size any clip in your head: take the bitrate, multiply by 450, and you have megabytes per hour.

Those figures are targets for the file you upload, not the file viewers stream. YouTube and similar sites re-encode everything into several lower bitrate versions. If your only goal is a file that looks clean after upload, matching the target is enough. Going far above it wastes space and upload time without a visible gain.

Worked example: a 10 minute 1080p clip

Take a 10 minute clip shot at 1080p and 30 fps, with stereo audio at 128 kbps. This is the default in the calculator.

1. Convert the length to seconds: 10 x 60 = 600 seconds.
2. Video data: 8 x 600 / 8 = 600 MB.
3. Audio data: 0.128 x 600 / 8 = 9.6 MB.
4. Add the two: 600 + 9.6 = 609.6 MB.
5. Add 3 percent for container overhead: 609.6 x 0.03 = 18.3 MB, so the file is 627.9 MB.

Per minute that is 627.9 / 10 = 62.8 MB. A 128 GB memory card holds 128,000 MB, so 128,000 / 62.8 = 2,038 minutes of this footage, which is 34 hours. That sounds generous until you compare it with the 4K case below, where the same card holds about four hours.

The upload side is easy to miss. The file is 627.9 MB, which is 5,023 megabits. On a 20 Mbps upload link that takes 5,023 / 20 = 251 seconds, or 4 minutes 11 seconds. The same file on a 5 Mbps link takes 16 minutes 45 seconds, because the time scales with the speed you have, not with the size of the file alone.

Worked example: 90 minutes of 4K

Now run a 90 minute 4K clip at 45 Mbps, with the same 128 kbps audio.

1. Seconds: 90 x 60 = 5,400.
2. Video: 45 x 5,400 / 8 = 30,375 MB.
3. Audio: 0.128 x 5,400 / 8 = 86.4 MB.
4. With 3 percent overhead: 30,461.4 x 1.03 = 31,375 MB, which is 31.4 GB.

A 128 GB card holds 128,000 / 31,375 = 4.08 files of that size, so four full recordings with a little room left. A 64 GB card holds two. If you shoot at 68 Mbps for 4K at 60 fps, the same 90 minutes becomes 47.4 GB and a 128 GB card holds two files with 33.3 GB to spare.

Uploading 31.4 GB on a 20 Mbps link takes 251,000 / 20 = 12,550 seconds, which is 3 hours 29 minutes. That is the number people forget when they plan a same day publish. Cutting the clip to 10 minutes before upload, rather than after, saves most of that wait.

Why the finished file is bigger than the math

The formula gives you the payload. Real files carry extra weight on top of it, and the gap can reach 10 percent.

• Variable bitrate. Most encoders spend more data on motion and less on still frames. The average may be 8 Mbps while busy scenes peak at 14 Mbps. A file built from a high motion scene runs larger than the formula predicts.
• Container overhead. The MP4 index, track headers and time stamps take 1 to 3 percent on a normal clip. Long recordings with many chapters can take more.
• Extra audio tracks. A second language or a commentary track at 128 kbps adds 57.6 MB per hour, the same as the first track.
• Metadata and thumbnails. Camera makers embed previews, gyro logs and timecode. These are small, often under 1 MB, but they explain part of the difference on short clips.
• Unit confusion. A file manager that reports GiB will show 4.8 percent less than a calculator working in GB. This one trips people up on every large file.

There is also the file system. A card formatted with a 128 KB cluster size rounds every file up to the next cluster, which matters for folders full of short clips and almost nothing for one long recording.

Practical rule: add 3 percent for a normal clip, 5 percent if the scene is busy or the clip runs over an hour, and treat the result as a floor rather than an exact figure.

Upload time is the other half of the question

Upload time comes from the same arithmetic, run in reverse. A megabyte is 8 megabits, so 1 GB is 8,000 megabits. Divide by your upload speed and you have the seconds.

The FCC raised its fixed broadband benchmark to 100 Mbps down and 20 Mbps up in 2024, with a long term goal of 1 Gbps down and 500 Mbps up. On a connection that just meets the benchmark, a 31.4 GB upload takes about three and a half hours, and that assumes the link runs at full speed the whole time. Wi-Fi, other devices in the house and the platform's own processing all add to it.

Two details change the estimate in practice. Many cable plans have upload speeds well below their download speed, often 10 to 35 Mbps, so check the upload figure rather than the headline number. And a wired connection usually beats Wi-Fi for a multi hour upload, since a dropped Wi-Fi link near the end means starting over on some sites. The FCC speed guide lists what common activities need.

Shrinking a file without wrecking the picture

Three levers cut the size, and they are not equal.

Codec. HEVC and AV1 store the same picture in less space than H.264. Encoding houses commonly report 30 to 50 percent savings at matched quality, which turns a 31.4 GB 4K file into something near 19 GB. The catch is playback: older phones, older TVs and some editors handle HEVC poorly, and AV1 support is thinner still. H.264 remains the safe choice when the file has to open anywhere.

Frame rate. Going from 60 fps to 30 fps removes half the frames, and with them close to half the data. For talking heads, screen recordings and most product video, 30 fps looks the same. Keep 60 fps for sport, gameplay and anything with fast pans.

Constant quality rather than constant bitrate. A quality setting, CRF in most encoders, spends data where it is needed. Values from 18 to 23 in H.264 and 23 to 28 in HEVC cover most delivery work. A higher number means a smaller file and softer detail, and the right value depends on the source more than on a rule.

Audio is rarely the problem. Stereo at 128 kbps is transparent for speech and fine for music in a video. Dropping it to 96 kbps saves 14.4 MB per hour, which is noise next to the video track. Do not re-encode a file twice to save space. Each pass throws away detail, and the second generation always looks worse than a single pass at the same size.

For a quick win with no quality cost, trim the start and end. Ten seconds of dead air at the head of a 4K clip costs 56 MB, and nobody watches it.

Reading the bitrate off your camera

Every camera and phone records at a bitrate it chose, and most of them will tell you the number if you look. On a mirrorless camera it sits in the recording menu next to the resolution, often as 100 Mbps or 200 Mbps. On a phone it hides behind the resolution picker, labeled something like 4K at 30 or 1080p at 60.

If the menu gives you the number, the math is one step: bitrate x 450 gives megabytes per hour. A camera set to 100 Mbps writes 45,000 MB, or 45 GB, for every hour of footage. At 200 Mbps it writes 90 GB. That is why a 128 GB card fills in under an hour and a half at the highest setting.

If the menu does not give you the number, measure it. Record 60 seconds, check the file size, and multiply. A one minute file of 375 MB means 22.5 GB per hour, which works out to 50 Mbps. That measured figure is more useful than any spec sheet, because it includes the audio and the container your camera writes.

One last check before you trust any of this: the size on the card is what matters for storage, and the size you upload is what matters for time. If your editor exports a different codec or resolution than the camera recorded, run the numbers again on the export settings rather than the capture settings. The export is the file that has to fit and the file that has to travel.