Video File Size Calculator

Everything about the size of a video comes down to one multiplication. A video stream and an audio stream each have a bitrate, a number of bits per second. Multiply the total by the number of seconds and divide by eight to get bytes. The rest of this calculator is that sentence turned into three questions: how big will it be, how long can it be, and what bitrate do I need? Knowing the answers before you export saves failed uploads and wasted storage.

The three questions

In File size mode you give the video and audio bitrates and the duration. In Playing time mode you give the bitrates and a size, and the calculator tells you how long fits. In Video bitrate mode you give a target size and a duration and it works out the video bitrate that fits after the audio is taken off. The formula is size = (video kbps + audio kbps) × 1,000 × seconds ÷ 8 × (1 + overhead). Kilobits per second here are 1,000 bits, as video tools use them.

A worked example

Press Sample: 8,000 kbps video, 192 kbps audio, a duration of 10 minutes and 2% overhead. The total is 8,192 kbps, so the stream data is 8,192 × 1,000 × 600 ÷ 8 = 614,400,000 bytes, and with 2% overhead 626,688,000 bytes: 627 MB, shown with 597.7 MiB beneath. Switch to Playing time with 500 MB and the same bitrates give about 8 minutes. Switch to Video bitrate with 500 MB for 10 minutes and you get roughly 6.3 Mbps for the picture, after the 192 kbps of sound and the overhead are taken off.

The planning table

The table shows what a given picture size needs at three quality levels: 0.06, 0.10 and 0.15 bits per pixel per frame, which are small, medium and high for H.264. It uses the frame rate you enter. For 1080p at 30 frames per second, Medium comes out at 6.2 Mbps and 491 MB for the ten minutes; High is 9.3 Mbps and 729 MB; 4K High is 37.3 Mbps and 2.87 GB. These are starting points: busy footage needs more bits, flat footage less, and new codecs get the same quality with fewer.

Units and overhead

Storage vendors use megabytes of a million bytes, while many systems show mebibytes of 1,048,576. The calculator shows both. Overhead depends on the container and on how frequently it stores index data; a percent or two is common, and live-streaming formats can add more. Set it to 0 to see the raw stream size, or raise it to leave a safety margin.

Edge cases

When the audio bitrate leaves nothing for the picture, Video bitrate mode says Not possible. A target size smaller than the sound alone cannot work. Variable-bitrate encoders such as the ones used by phones average the bitrate you set, so the real file lands near the estimate but not exactly. Lossless and intraframe codecs such as ProRes do not follow a bits-per-pixel rule.

Limits

This is arithmetic, not an encoder: it does not create video or check an existing file. The table uses fixed quality levels. Because everything is computed in the page, no data is sent anywhere.

Related tools

• Compress Video uses the same target-size arithmetic to re-encode.
• Stream Bitrate Calculator matches a bitrate to an upload speed.
• Audio File Size Calculator does the same for sound-only files.
• Video Cutter & Trimmer shortens a video so it fits a size limit.