Video file size calculator

What is the formula?

Size in megabytes is bitrate in megabits per second multiplied by seconds, divided by 8, because eight bits make a byte. Audio adds its own bitrate, usually a small share. This calculator adds both.

Example: 8 Mbps video plus 192 kbps audio over 60 seconds is (8,000 + 192) × 60 ÷ 8 ÷ 1,000, about 61.4 MB.

Why is the result only an estimate?

Many encoders use variable bitrate, which spends more bits on busy scenes and fewer on still ones, so the real file differs from the average you set. Containers also add a small overhead. Treat the output as a planning number, then check the real file.

• Constant bitrate gets closest to the estimate.
• Talking-head footage compresses well, so files often come out smaller than a busy scene would.
• Two-pass encodes aim for an average and land closer to a target size.

When is this useful?

Use it when a platform or email limit caps your upload size, when you plan storage for a batch of exports, or when you compress a render. A short vertical reel from a Glass render, for instance, is small enough that size rarely matters, while a long widescreen video may need a lower bitrate to fit a limit.

How do you lower file size without ruining quality?

• Lower the bitrate a step at a time and watch the result at full size.
• Keep resolution sensible for the platform rather than exporting larger than needed.
• Use a modern codec if your target accepts it, since it needs fewer bits for similar quality.
• Trim dead air before you export; every second costs bits.