How to use the Video Bitrate Estimator and File Size Calculator
- Enter length and shape. Type the duration, choose a resolution preset or type a custom width and height, and set the frame rate you export at.
- Choose a codec. Pick H.264, H.265, VP9 or AV1. Newer codecs are assumed to need a lower bitrate for similar looking video.
- Set quality or size. Use target quality for a recommended bitrate, or target file size to find the bitrate that makes the file that size.
- Pick an audio bitrate. Choose 96 to 256 kbps, or none. The audio table shows how much each option costs in size.
- Read the fit table. See which networks accept the file size, and the highest video bitrate that would still fit each cap, then export with that bitrate in your editor.
How the bitrate and size maths works
What it calculates
Recommended video bitrate in Mbps = bits per pixel x width x height x frames per second / 1,000,000. File size in MB = (video Mbps + audio kbps / 1000) x seconds / 8. The reverse mode solves the same sum for the video bitrate: size x 8 / seconds - audio kbps / 1000. The detail level label compares your bits per pixel with the low, medium and high values of the codec you chose.
Where the size caps come from
X: 8 GB for free accounts and 16 GB for Premium, from the X developer documentation on media best practices. Instagram Reels: 300 MB, from the Instagram Graph API reference for media. Threads: 1 GB, from the Threads API posting documentation. Bluesky: 300 MB, from the Bluesky video embed lexicon. Mastodon: 99 MB, the VIDEO_LIMIT in the Mastodon source code. Instances can change it. All were checked in October 2026.
We read each cap as decimal megabytes, which is the cautious reading when a source does not say whether it means 1,000,000 or 1,048,576 bytes.
Limitations
The bitrate numbers are a rule of thumb. Footage with fast motion, film grain or fine detail needs more than a talking head at the same resolution, and a variable bitrate export averages out around your target. Container overhead is not added, so leave a little room under a cap. This tool checks file size only, not length or aspect ratio limits.
Frequently asked questions
How do you work out the file size of a video?
Add the video and audio bitrates, multiply by the duration in seconds and divide by 8 to get bytes. For example, 60 seconds at 5 megabits per second is 300 megabits, which is 37.5 megabytes before audio. The tool uses decimal megabytes, where 1 MB is 1,000,000 bytes.
Where do the recommended bitrates come from?
They come from a simple rule of thumb that you can see on the page: bits per pixel per frame multiplied by pixels per second. We use 0.05, 0.09 and 0.15 for low, medium and high H.264, and scale other codecs down. They are our working assumptions, not a standard and not a rule from any network.
Will the network keep my bitrate?
Do not count on it. Networks may re-encode uploads, so viewers can see a different file from the one you sent. We do not know how any network does this inside, so the tool says nothing about it. What you control is the upload: a clean source at a sensible bitrate gives the network good material to work from.
What does the max bitrate that fits mean?
It is the cap in megabytes, times 8, divided by the duration, minus the audio bitrate. Any video bitrate at or under that number keeps the file inside the cap. If it is lower than the recommended bitrate, you either shorten the video, lower the resolution, or accept a softer picture.
Which size caps does it check?
X: 8 GB for free accounts and 16 GB for Premium. Instagram Reels: 300 MB. Threads: 1 GB. Bluesky: 300 MB. Mastodon: 99 MB by default, though a server can set another limit. The support notes name the source of each.
Does a higher frame rate need a higher bitrate?
In this rule of thumb, yes, in direct proportion: 60 frames per second asks for twice the bitrate of 30 at the same bits per pixel. Real encoders do not scale quite that straight because neighbouring frames are similar, so treat 60 fps results as a generous start.