Video File Size Calculator

You need a five-minute 1080p clip under 25 MB for email. Should you export at 2 Mbps or 720p? A back-of-napkin estimate saves another round of trial exports. When the cap is fixed, compress video to target size on Mac skips manual iteration.

Estimates are planning tools, not guarantees. Always export a short sample before committing a hour-long render.

What you need to estimate size

Four inputs drive most delivery files:

Input	Example
Duration	300 seconds
Video bitrate	5 Mbps
Audio bitrate	0.128 Mbps (128 kbps)
Container overhead	Small; often ignored for estimates

Codec choice (H.264 vs HEVC) changes how many Mbps you need for the same look, not the formula itself.

If you only know file size and duration from an existing clip, divide to learn its average bitrate: (MB × 8) ÷ seconds. That reverse-engineering helps when copying settings from a reference upload.

The core formula

Size (bits) ≈ (video bitrate + audio bitrate) × duration

Convert to megabytes:

MB ≈ (video Mbps + audio Mbps) × seconds ÷ 8

Example:

• Video: 8 Mbps
• Audio: 0.128 Mbps
• Duration: 120 s

(8.128 × 120) ÷ 8 = 121.9 MB

Add 1 to 3 percent for container mux if you are cutting close to a hard cap.

Reverse the math when you have a cap: allowed Mbps ≈ (MB × 8) ÷ seconds. For 25 MB and 120 s, total bitrate is about 1.67 Mbps, which pushes you toward 720p for acceptable quality. Email caps vary; see email attachment size limits .

Related: how long is a 10 MB video .

Quick reference tables

H.264, 128 kbps audio, approximate video size:

Duration	2 Mbps	5 Mbps	8 Mbps
30 s	~8 MB	~19 MB	~30 MB
1 min	~16 MB	~38 MB	~61 MB
5 min	~77 MB	~192 MB	~307 MB
10 min	~154 MB	~384 MB	~614 MB

1080p talking-head content often looks acceptable between 4 and 8 Mbps. Screen recordings with text may need higher Mbps at the same resolution or a 720p downgrade.

Add 5 to 10 percent headroom below a hard cap if the portal measures megabytes in decimal MB while your OS shows mebibytes. Round down when the upload widget says “10 MB max.”

Resolution and frame rate multipliers

No single multiplier is exact because content complexity matters, but planning guides help:

Change	Size impact (typical)
1080p to 720p	~40 to 55 percent smaller at same quality target
4K to 1080p	~75 percent smaller pixel count
60 fps to 30 fps	Up to ~40 to 50 percent smaller at same CRF
H.264 to HEVC at same look	~30 to 50 percent smaller

See frame rate in video and H.264 vs H.265 .

Audio bitrate to include

Do not forget audio when the cap is tight.

Audio setting	Bitrate
Voice mono	64 to 96 kbps
Voice stereo	96 to 128 kbps
Music	160 to 192 kbps

128 kbps AAC adds about 1 MB per minute. On a 10 MB budget that matters.

Stereo music needs more headroom than mono voice. Do not strip audio to unusable levels just to shave a megabyte off video.

From estimate to actual export

1. Pick target MB and duration → solve for Mbps.
2. Choose resolution and codec that can look good at that Mbps.
3. Export a 10-second sample at those settings.
4. Scale: sample MB × (total duration ÷ sample duration).
5. Adjust quality up or down.

If math says 2 Mbps at 1080p but text looks soft, trim more or accept 720p instead of crushing bitrate.

Keep a spreadsheet of sample exports once: duration, resolution, Mbps, final MB. Reuse that row when the same portal appears monthly.

Practical export walkthroughs: compress video on Mac , compress video on Windows . For upload ceilings on social platforms, see YouTube video size limits . Bitrate concepts: what is video bitrate . Ticket attachments: compress video for email on Mac .

Round duration up to the nearest five seconds when planning live events. A 58-minute talk plus intro/outro crosses hour boundaries that affect backup and upload scheduling.

Using GetCompress

Skip the spreadsheet: set target file size, duration is read from the clip, and GetCompress iterates encoder settings locally until the export nears your cap. Preview quality, compare before/after megabytes, batch multiple clips with the same preset, and save calculator-free workflows for recurring limits.

The calculator still helps you sanity-check whether a five-minute 1080p clip can ever fit a 25 MB email cap before you spend time editing.