By Ahsan Khowaja · Updated 27 October 2026
How to use the video file size calculator
- Choose File size from bitrate and length to estimate a file, or How much video fits on a card or drive to turn a capacity into recording time.
- Enter the video bitrate. Your camera's manual or on-screen info lists it per recording mode, your editor's export panel shows it, and for an existing file a media player's information panel reads it from the stream. Mbps and kbps are both accepted.
- Enter the audio bitrate in kbps, or 0 for silent footage.
- Enter the running time, or the card size in GB or TB.
Sizes are shown in decimal units, where 1 GB is 1,000,000,000 bytes, because that is how cards, drives and cloud plans are sold. The "as a computer may show it" row gives the binary figure (GiB, 1,073,741,824 bytes) that Windows labels "GB", so the number you see in Explorer will match that row, not the first one.
The formula: bitrate × time ÷ 8
A video's size depends on only two things: how much data it uses per second (the bitrate) and how many seconds it runs. Resolution, frame rate and codec matter only through the bitrate they lead to.
File size (bytes) = (video bitrate + audio bitrate) in bit/s × seconds ÷ 8
The ÷ 8 converts bits to bytes. In everyday units, an 8 Mbps stream writes 1 MB per second, 60 MB per minute and 3.6 GB per hour, and every other bitrate scales in proportion. So the video file size calculator bitrate figure is the one input that matters: double it and the file doubles, whatever the resolution says.
Worked examples
- 10 minutes at 8 Mbps + 128 kbps audio: 8,128,000 bit/s × 600 s = 4,876,800,000 bits ÷ 8 = 609,600,000 bytes, which is 609.6 MB (581.36 MiB on Windows). That is 60.96 MB per minute or 3.66 GB per hour.
- A 2-hour 1080p film at the same settings: 8,128,000 × 7,200 ÷ 8 = 7,315,200,000 bytes, about 7.32 GB (6.81 GiB).
- 30 minutes of 4K at 45 Mbps + 384 kbps audio: 45,384,000 × 1,800 ÷ 8 = 10,211,400,000 bytes, about 10.21 GB, or 20.42 GB per hour.
- A 30-second clip at 6 Mbps + 160 kbps: 6,160,000 × 30 ÷ 8 = 23,100,000 bytes, 23.1 MB.
GB per hour of video at common bitrates
This table is the formula applied to one hour of footage. The bitrates in the first block are YouTube's recommended upload encoding settings for SDR video at 24–30 fps, with a 128 kbps audio track added; the higher-frame-rate and camera rows use round figures for comparison.
| Footage | Video bitrate | GB per hour (with 128 kbps audio) | Per 10 minutes |
|---|---|---|---|
| 720p, 30 fps (YouTube upload) | 5 Mbps | 2.31 GB | 385 MB |
| 1080p, 30 fps (YouTube upload) | 8 Mbps | 3.66 GB | 610 MB |
| 1080p, 60 fps (YouTube upload) | 12 Mbps | 5.46 GB | 910 MB |
| 1440p, 30 fps (YouTube upload) | 16 Mbps | 7.26 GB | 1.21 GB |
| 4K, 30 fps (YouTube upload, low end) | 35 Mbps | 15.81 GB | 2.63 GB |
| 4K, 30 fps (YouTube upload, high end) | 45 Mbps | 20.31 GB | 3.38 GB |
| Camera recording mode | 50 Mbps | 22.56 GB | 3.76 GB |
| Camera recording mode | 100 Mbps | 45.06 GB | 7.51 GB |
| Camera recording mode | 200 Mbps | 90.06 GB | 15.01 GB |
Use it as a 1080p video file size calculator or a 4K video file size calculator by reading across the row, or type the bitrate into the calculator for a different length. Phone recordings usually sit well above YouTube's upload figures, so a 1080p clip straight from a phone is often 2× the "1080p" row.
Video size calculator by resolution: why the answer is "it depends"
People search for a 720p video size calculator or an MP4 file size calculator expecting one number per resolution. There isn't one. 1080p only fixes the frame at 1920 × 1080 pixels; the file size comes from the bitrate the encoder was given, and the same minute of 1080p can be 30 MB from a streaming service or 400 MB from a camera. The container (MP4, MOV, MKV) adds a fraction of a percent and otherwise makes no difference.
What resolution does do is set a sensible bitrate range: more pixels need more data to look clean, which is why the recommendations above climb from 5 Mbps at 720p to 35–45 Mbps at 4K. So the honest way to estimate by resolution is to pick a bitrate that suits it and run the formula, which is what the table does. If you know the file size but not the bitrate, the bitrate calculator solves the formula the other way.
How long a card or drive records for
The second mode divides the capacity by the total bitrate:
Recording time (seconds) = capacity (bytes) × 8 ÷ (video bitrate + audio bitrate)
- A 32 GB card at 25 Mbps with no audio: 256,000,000,000 bits ÷ 25,000,000 = 10,240 s, which is 2 h 50 min 40 s, or 5 min 20 s per GB.
- A 256 GB card at 100 Mbps with 320 kbps audio: 2,048,000,000,000 ÷ 100,320,000 = 20,415 s, about 5 h 40 min, with each hour of footage taking 45.14 GB.
- 1 GB at 8 Mbps + 128 kbps audio holds 16 min 24 s.
Card makers quote decimal capacity, and formatting reserves a little of it, so expect a few percent less in practice. Many cameras also split recordings into 4 GB files on cards formatted as FAT32, which doesn't change the total but does change how many files you get. The GB to TB converter and MB to GB converter sort out the units if a drive is labelled differently from the way you think in.
Checking the estimate against a real file
The calculator gives an exact answer for a constant bitrate. Most files use variable bitrate, where the encoder spends more on motion and less on still shots, so a real file can land 10–20% either side of the estimate for the "average" bitrate the camera quotes. Two ways to tighten the number:
- Record or export a one-minute test and read its size in the file's properties, then multiply by the length you plan. Your phone does this for you: the iPhone's Settings › Camera › Record Video screen shows an approximate size per minute for each mode.
- For a file you already have, read the bitrate from the player's media information and the length from the clock, then run them through here.
Making a video smaller is a separate job from estimating it. Lowering the bitrate is the lever that shrinks files; lowering the resolution only helps because it lets you lower the bitrate without the picture breaking up. For stills rather than video, our image compressor does the same job in the browser.
