Work Out Video File Size, Bitrate or How Long a Video Can Be

How to use the video file size calculator

Pick one of the three modes at the top, fill in what you know, and the answer updates as you type.

• File size tells you how big a video will be. Enter its length, then either choose a resolution, frame rate and quality, or type an exact bitrate if your camera or export settings show one.
• Max length tells you how long a video can run inside a size limit, like 25MB for an email attachment or 2GB for a cloud upload.
• Bitrate tells you how many bits per second a size limit leaves you for a clip of a given length, and which resolution still looks clean at that budget.

If you already have the video, click "Fill in from a video file". The calculator reads the clip's length and size, works out its average bitrate and switches to exact mode, so you can see what the same video would weigh at a different length. It only reads those two numbers from the file on your device.

How video file size is calculated

Every video file size comes from one formula: bitrate times duration, divided by eight to turn bits into bytes.

file size = (video bitrate + audio bitrate) × seconds ÷ 8

Take a 5-minute 1080p clip at 8 Mbps with 128 kbps audio. That's 8.128 million bits every second, times 300 seconds, divided by 8: about 305 million bytes. The calculator shows 295 MB for the same clip, and the gap comes from two details I build into every number on this page.

First, I count 1 MB as 1,048,576 bytes, the way Windows does and the way the compressors on this site do. macOS Finder and most websites count 1 MB as 1,000,000 bytes, so Finder shows the same file about 5% bigger. Second, I add about 1.5% for the MP4 container itself: the index that tells a player where each frame sits, plus the track headers. On a short clip it barely matters. Near a hard limit like Discord's 20MB, it decides whether the upload goes through.

Run the formula backwards and you get the bitrate a limit allows: bitrate = size × 8 ÷ seconds. That's all the Bitrate mode does, before it subtracts the audio and checks which resolution the leftover budget can carry.

How long is a 10MB, 25MB, 100MB or 1GB video?

This table uses the calculator's Good quality at 30fps in H.264, with 128 kbps audio. That's a sensible target for footage straight out of a camera or a phone.

You'll find longer times on my 10MB video compressor page, and both pages are right. The compressor tables come from real phone clips that the phone already compressed in HEVC, and a clip like that has lost the sensor noise and fine texture that cost the most bits. The compressor can push it lower than this table's Good setting and still keep a clean picture. Treat this table as the safe answer for fresh footage, and the compressor pages as the answer for a typical phone video you want to send.

Switch the quality to Lean and every time in the table grows by about a third. Switch the frame rate to 60fps and every time shrinks by about a third.

Video bitrate calculator: what a size limit leaves you

A size limit and a clip length fix the bitrate, and nothing you change in an export dialog gets around that. Here is what a 25MB email attachment leaves for the video track once 128 kbps goes to audio:

The resolution column is where most people go wrong. Exporting a 3-minute clip at 1080p into 25MB gives the encoder 1 Mbps to paint two million pixels per frame, and the result turns to blocks. At 480p the same 1 Mbps covers a fifth of the pixels and looks clean. When the budget is tight, a smaller frame always beats a starved big one. The Bitrate mode marks each resolution as Looks good, Acceptable or Too soft for exactly this reason.

When you know the size you need, the button under the result takes you to the matching compressor. It sends 8MB to the 8MB video compressor, 20MB, 50MB and 500MB to the Discord video compressor, 25MB to the email video compressor, and anything else to the main video compressor, where you can type any target size.

What Lean, Good and High mean

Bitrate alone doesn't predict quality. A bitrate that looks sharp at 720p looks smeared at 4K, because the 4K frame has nine times as many pixels to cover. So the quality setting doesn't pick a bitrate. It picks a number of bits per pixel per frame, and the calculator multiplies that by the resolution and frame rate you chose:

• Lean is 0.075 bits per pixel, the lowest point where I still call the picture clean on normal footage.
• Good is 0.10, the level my compressor's Balanced setting aims for.
• High is 0.15, where the result looks the same as the source in normal viewing.

Multiplied out for H.264 at 30fps, those three levels give these bitrates:

Frame rate doesn't double the cost. At 60fps, consecutive frames sit closer together in time and less changes between them, so 60fps needs about 1.5 times the bitrate of 30fps, the same step YouTube uses in its upload recommendations. A minute of 1080p60 at Good comes to about 69 MB. I explain where these numbers come from, and how they compare with YouTube's, in my video bitrate chart.

How the codec changes file size

All the tables above assume H.264, the codec every phone, browser and TV plays. Newer codecs carry the same picture in fewer bits, and the Codec setting divides the bitrate by these factors:

An iPhone on its default "High Efficiency" camera setting records HEVC, which is why a phone clip often weighs less than the H.264 estimate. If you convert that clip to H.264 so an older PC can play it, expect the file to grow unless you also lower the resolution.

Why your real file can differ from the estimate

The calculator gives you the size of a video encoded at a fixed average bitrate, which is what a target-size compressor or a two-pass export produces. A few situations move a real file away from that number:

• Quality-based exports. HandBrake's RF slider, FFmpeg's CRF and most phone cameras hold quality steady and let the bitrate float. A calm talking-head video comes out far smaller than a shaky concert clip at the same setting, so no calculator can predict their size exactly. Fill in from the finished file to see its real average.
• Busy footage. Water, foliage, confetti, fast games and low-light grain all need the top of each range. Screen recordings and slides need the bottom.
• Extra tracks. A second audio language, a commentary track or embedded subtitles all add to the total. Choose None for audio if the clip is silent.

For anything with a hard limit, aim a few percent under it. My compressors aim about 7% under the target on the first pass for the same reason.

Frequently asked questions