Estimate video file size from bitrate and duration, or find the bitrate that fits a target size — with email and upload presets.
AI-powered audio review & delivery for voice production teams
Calculating, not compressing.
This page does the size math only — it never uploads or re-encodes your video. To actually shrink a file, use a dedicated video compressor (coming soon). Need a bitrate to start from? Try the Video Bitrate Calculator. Working out export durations? The Timecode Calculator adds them up. Reducing an audio file instead? See the Audio Bitrate Converter.
Video at Mbps plus a kbps audio track, over .
These are decimal megabytes (1 MB = 1,000,000 bytes). Your OS reports binary MiB, so it may show this file as roughly 5% smaller. Add about 2–5% on top for container (MP4/MOV) and muxing overhead — treat the number as a close estimate, not an exact byte count.
File size is bitrate multiplied by time. A video stream spends a fixed number of bits on every second of footage (its bitrate), the audio track spends its own, and the file is just the sum over the whole duration:
size (bytes) = (video bitrate + audio bitrate) × duration ÷ 8
The ÷ 8 converts bits to bytes. For example, a clip at 10 Mbps of video plus a 320 kbps audio track running one minute works out to (10,000,000 + 320,000) × 60 ÷ 8 ≈ 77 MB.
Two practical notes the calculator builds in. First, these are decimal megabytes (1 MB = 1,000,000 bytes), which is how drive makers and most upload limits count; your operating system reports binary MiB (1 MiB = 1,048,576 bytes), so it will show the same file as roughly 5% smaller. Second, the raw math is the elementary stream — a real MP4 or MOV adds about 2–5% for the container, muxing and metadata. Treat the result as a close estimate, not an exact byte count.
It is a common surprise: resolution does not directly set file size, bitrate does. A 4K clip and a 1080p clip encoded at the same bitrate occupy the same space. What changes is how that bitrate looks — spread 8 Mbps across 4K's eight million pixels and detail falls apart, while the same 8 Mbps over 1080p looks clean. That is why higher resolutions and frame rates are given more bitrate, and it is the bitrate increase — not the pixel count itself — that grows the file. If you want a recommended bitrate for a given resolution, codec and quality, use the Video Bitrate Calculator; this page turns whatever bitrate you choose into a size, and back again.
To hit a ceiling — a 25 MB email attachment, a Discord upload, a hard client spec — work backwards. The target size and the duration fix a total bit budget; subtract the audio track and what remains is the video bitrate you can afford:
video bitrate = (target MB × 8,000,000 ÷ duration in seconds) − audio bitrate
The "Fit to target size" mode does this for you and warns when a target is impossible — for instance when the audio track alone already exceeds the budget, or when the leftover video bitrate is too low to look acceptable. Remember this is the math: actually producing that smaller file means re-encoding it in an editor or a dedicated video compressor (coming soon to VoiceDeck). This page tells you the number to aim for; it does not compress the file itself.
File size equals bitrate times duration. Add the video bitrate and the audio bitrate, multiply by the running time in seconds, and divide by 8 to convert bits to bytes: size = (video_bps + audio_bps) × seconds ÷ 8. For example, 10 Mbps of video plus a 320 kbps audio track over one minute is about 77 MB. The result is in decimal MB (1 MB = 1,000,000 bytes); real MP4/MOV files add roughly 2–5% for container overhead.
It depends entirely on the duration, because 100 MB is a fixed bit budget spread across however long the clip runs. Over 2 minutes with a 320 kbps audio track, 100 MB holds about 6.3 Mbps of video; over 5 minutes it drops to about 2.3 Mbps. Use the "Fit to target size" mode above — enter 100 as the target and your duration — to get the exact number.
Three things make files big: a high bitrate, a long duration, and an editing/intraframe codec. Higher resolutions and frame rates feel like the cause, but they only matter because they push the bitrate up. Mezzanine codecs like ProRes or DNxHR store every frame in full at a fixed, very high data rate — great for editing, enormous on disk. For delivery, export H.264 or H.265 at a sensible bitrate and the file shrinks dramatically.
Bitrate controls file size directly; resolution does not. A 4K file and a 1080p file at the same bitrate are the same size — the 4K one just looks worse at that bitrate because the bits are spread over four times the pixels. That is why higher resolutions are given more bitrate, and it is the extra bitrate, not the resolution, that grows the file. Pick the bitrate and this calculator gives you the size.
Most email services cap attachments around 25 MB (Gmail and Outlook), and chat apps are often lower — Discord 25 MB, WhatsApp around 16 MB. Use the "Fit to target size" mode to find the bitrate that lands under the limit for your clip's length, then re-export at that bitrate (or shorten the clip). If even the lowest watchable bitrate won't fit, share a link instead of an attachment. This tool calculates the target; it does not compress the file.
Not sure what bitrate to use? Get a recommended rate from resolution, frame rate and codec.
Add and subtract timecode and convert between frames and duration across every frame rate.
Working with audio instead? Convert an MP3 or WAV file to a different audio bitrate.
VoiceDeck adds AI-powered audio & video review and delivery for your whole team — so every file ships in spec, automatically.
