A video file size calculator converts a bitrate and a duration into bytes, or reverses the calculation to find the bitrate that will fit inside a fixed capacity. Those two directions cover most practical video planning: how much card or drive a shoot needs, and what encoder setting will squeeze a finished edit onto a disc, into an upload limit or under an email attachment cap.
Arb Digital publishes this in its free tools library. Two boundaries are worth stating up front. This page does not process a video file — it does arithmetic on numbers you type, which is what makes it useful before anything has been recorded. And it is the storage-side companion to the streaming bitrate calculator: that page answers what bitrate a live platform needs and what upload headroom it demands, while this one answers what a recording will consume on disk. Same units, opposite question.
What This Video File Size Calculator Does
In size mode it multiplies the combined video and audio bitrate by the duration and converts to bytes. In bitrate mode it inverts that: you give it a target size and a duration, and it returns the total bitrate available, then subtracts the audio allocation to leave the video bitrate you should set in the encoder.
The results grid separates the video and audio tracks, because the split surprises people in both directions. At a 12 Mbps video bitrate, a 192 kbps audio track is 1.6% of the file and effectively free. At a 1 Mbps video bitrate for a screen recording, that same audio track is 16% of the file and is worth reducing.
The bits-per-pixel figure is the quality-efficiency measure. It divides the video bitrate by pixels per second, and it makes bitrates comparable across resolutions and frame rates in a way that raw megabits per second cannot. Twelve megabits is generous at 1080p30 and starvation at 4K60, and the bits-per-pixel number says so directly.
How to Use It
- Choose the mode that matches your constraint. If the capacity is fixed — a disc, an upload cap, a card — solve for bitrate. If the encoder settings are fixed, solve for size.
- Enter duration in minutes, including handles. A 45-minute programme captured with pre-roll and safety padding is usually 55 minutes of actual recording, and cards fill to the real number.
- Set the audio bitrate honestly. Multichannel audio at 384 or 512 kbps is a materially different allocation from a 128 kbps stereo track, and at low video bitrates it is a significant share.
- Select the resolution and frame rate for the bits-per-pixel readout. They do not change the file size arithmetic — only the assessment of whether the bitrate is adequate.
- Check the units selector before comparing against hardware. Drives and cards are sold in decimal gigabytes; many operating systems report binary gibibytes, and the gap at that scale is about 7%.
The Formula / How It's Calculated
Both directions come from one relationship:
File size in bytes = (video bitrate + audio bitrate) × duration in seconds ÷ 8
Rearranged for the reverse problem: total bitrate = target size in bytes × 8 ÷ duration in seconds, and video bitrate = total bitrate − audio bitrate. Bits per pixel is video bitrate ÷ (width × height × frames per second).
Worked example, matching the values the page loads with. A 45-minute recording is 2,700 seconds. At 12 Mbps video and 192 kbps audio the combined rate is 12,192,000 bits per second, so the file is 12,192,000 × 2,700 ÷ 8 = 4,114,800,000 bytes, or 4.11 GB — 3.83 GiB as a file manager would show it. The video track alone accounts for 4.05 GB and the audio track for 64.8 MB, which is 1.6% of the total. Per minute of footage that is 91.44 MB. At 1080p30 the video bitrate spreads across 1,920 × 1,080 × 30 = 62,208,000 pixels per second, giving 0.193 bits per pixel.
Reversing it: to fit the same 45 minutes into exactly 4.00 GB, the total bitrate available is 4,000,000,000 × 8 ÷ 2,700 = 11,851,852 bits per second, or 11.85 Mbps. Subtracting the 0.192 Mbps audio allocation leaves a video bitrate of 11.66 Mbps. The Library of Congress format description for MPEG-4, Advanced Video Coding (Part 10) (H.264) documents the codec most of these numbers assume.
Resolution Does Not Appear in the Formula — and Why That Confuses People
This is the section that resolves the most common misunderstanding about video storage.
A 4K file is not larger than a 1080p file because it is 4K. It is larger because it was encoded at a higher bitrate. Encode 4K footage at 12 Mbps and it produces exactly the same file size as 1080p footage at 12 Mbps of the same duration — the 4K version will simply look considerably worse, because the same bits are being spread across four times as many pixels.
That is what the bits-per-pixel readout captures. At 1080p30, 12 Mbps gives 0.193 bits per pixel, which is comfortable for most content. At 4K30 the same 12 Mbps gives 0.048 bits per pixel, and compression artefacts become visible in anything with motion or fine detail. Getting back to 0.193 bits per pixel at 4K30 would require about 48 Mbps — four times the bitrate, four times the storage.
Frame rate behaves the same way. Doubling from 30 to 60 fps doubles pixels per second, so holding quality constant requires more bitrate — though in practice not double, because consecutive frames at 60 fps are more similar to each other and inter-frame compression exploits that. A common working figure is around a 1.5× increase rather than 2×.
The practical conclusion is that resolution and frame rate are decisions about how much bitrate you need, and bitrate and duration are what determine the file. Anyone planning storage should decide quality first, derive the bitrate, and only then compute size.
Codec Choice Is Worth More Than Any Other Setting
The same visual quality costs very different amounts of bitrate depending on the codec, and the differences are large enough to dominate every other decision.
H.264 is the baseline: universally supported, hardware-decoded on essentially everything, and the assumption behind most published bitrate tables. HEVC reaches comparable quality at roughly half the bitrate on typical content, and AV1 improves on HEVC again. Halving the bitrate halves the file, so a codec change alone can do what no amount of setting adjustment will.
The cost is compatibility and encoding time. AV1 encoding is computationally expensive, and hardware decode support, while now widespread, is not universal on older devices. HEVC carries licensing complexity that has slowed its adoption in browsers. A file that will not play is not smaller in any useful sense.
One more distinction matters for planning: constant bitrate against variable bitrate. CBR holds the rate fixed, which makes file size perfectly predictable and is why live streaming uses it — this calculator's arithmetic is exact for CBR. VBR spends more bits on complex scenes and fewer on simple ones, producing better quality per byte but a file size that only matches the estimate on average. For VBR encoding, treat the target bitrate as an average and expect real files to land within roughly 10% either side. YouTube's recommended upload encoding settings publish target bitrates per resolution and frame rate that are a useful reference point for the values to enter here.
Planning Cards, Drives and Delivery
Three recurring problems, each solved from a different direction.
Card capacity on a shoot. Take the per-minute figure and multiply by the total recorded minutes, not the finished runtime. Multi-camera shoots multiply again. Then leave headroom — filling a card completely risks a truncated final clip, which is the one file you cannot re-shoot. Camera codecs are also far less efficient than delivery codecs: a professional intra-frame recording format can run at ten times the bitrate of the H.264 file that eventually ships.
Post-production storage. The camera originals are only the beginning. Proxies, render caches, graded masters and multiple deliverable versions typically total two to four times the original footage. The data storage converter handles the unit arithmetic once these reach terabytes.
Fitting a hard limit. This is what bitrate mode is for. Set the target slightly below the true limit — container overhead for the MP4 or MKV structure, chapter data and subtitle tracks adds a small percentage that the pure bitrate calculation ignores. Aiming at 3.9 GB for a 4 GB ceiling is the safe habit. If the required bitrate comes out uncomfortably low for the resolution, the fix is usually to reduce the resolution rather than accept a starved encode at full size, since a clean 1080p file looks better than a badly compressed 4K one at the same byte count.
Arb Digital plans and produces video content built around search demand and completion rates, so the footage you store is the footage that gets watched.
See Content Marketing Services Talk to Arb DigitalCommon Mistakes to Avoid
- Assuming resolution determines file size — bitrate and duration alone determine bytes. Resolution determines how much bitrate you need to look acceptable, which is a different question.
- Ignoring the audio track at low bitrates — 192 kbps is 1.6% of a 12 Mbps file and 16% of a 1 Mbps screen recording.
- Aiming exactly at a hard limit — container overhead, subtitles and chapter data push a file slightly past a bitrate-only estimate, so leave a few per cent of margin.
- Treating a VBR target as exact — variable bitrate hits the target on average, not per file, so expect a spread of roughly ten per cent around the estimate.
- Planning storage from finished runtime — cards fill with everything recorded, including takes, pre-roll and multiple camera angles, which is usually several times the final edit.
Related Free Tools From Arb Digital
Work out live encoder settings with the streaming bitrate calculator, convert units with the data storage converter or the bandwidth converter, and size stills for the same shoot with the image file size calculator. The aspect ratio calculator handles framing and scaling arithmetic, the data usage calculator covers what viewers consume, and the video completion rate calculator measures whether the footage held attention. Everything else is in the free online tools hub.
Frequently Asked Questions
No. It performs arithmetic on values you type, so it works before anything has been recorded. That is the point — it is a planning tool for sizing cards, drives and uploads rather than a utility that acts on an existing file.
Only because 4K is normally encoded at a higher bitrate. At the same bitrate and duration the two produce identical file sizes, and the 4K version simply looks worse because the same bits are spread over four times as many pixels.
This page answers what a recording consumes on disk. A streaming bitrate calculator answers what encoder settings a live platform needs and how much upload headroom that requires. The units are the same and the question is the opposite.
For typical H.264 delivery, somewhere around 0.1 to 0.2 bits per pixel is a reasonable working range for general content, with animation and static screen recordings needing far less and high-motion sport needing more. Efficient codecs such as HEVC and AV1 look acceptable at roughly half those values.
Container overhead. The MP4 or MKV structure, index tables, chapter markers and subtitle tracks all add bytes that a pure bitrate calculation does not include. It is normally a small percentage, which is why targeting slightly under a hard limit is the safe approach.
A great deal. HEVC typically reaches comparable quality at around half the bitrate of H.264 on similar content, and AV1 improves further. Because file size is directly proportional to bitrate, halving the bitrate halves the file — more than any other single setting will achieve.
Constant bitrate makes file size exactly predictable and is what live streaming requires. Variable bitrate gives better quality for the same average size by spending more bits on complex scenes, at the cost of a file size that only matches the target on average.
Multiply the per-minute figure by everything actually recorded rather than the finished runtime, then multiply again for each camera. Add two to four times over for proxies, caches and deliverable versions in post-production, and leave headroom rather than filling cards to capacity.
