How is video file size calculated from bitrate?

File size equals bitrate times duration. Bitrate is measured in megabits per second, so multiply by the number of seconds and divide by eight to get megabytes. A 100 Mbps clip for 60 seconds is 100 times 60 divided by 8, which is 750 megabytes.

What is the difference between megabits and megabytes?

Bitrate is quoted in megabits per second, written Mbps with a lowercase b. File size is in megabytes, written MB with an uppercase B. There are eight bits in a byte, so you always divide the bitrate figure by eight to convert to storage units.

Why are ProRes and RAW files so large?

Intra-frame and lightly compressed formats like ProRes 422 HQ and camera RAW store each frame nearly independently to preserve quality for editing. ProRes 422 HQ at 4K runs around 880 Mbps, while compressed delivery codecs like H.265 manage similar quality at a tenth of the bitrate.

How do I find the bitrate for a target file size?

Switch the tool to reverse mode and enter your target size and duration. It divides the size in megabits by the duration in seconds to give the bitrate. This is useful when fitting an export to an upload limit or a fixed card capacity.

Does frame rate change the file size?

Only indirectly. Most codecs are specified at a target bitrate that already assumes a frame rate, so higher frame rates usually carry a higher bitrate to keep quality constant. If you fix the bitrate, the file size depends only on bitrate and duration, not frame rate.

What is the Video Bitrate & Storage Calculator?

Calculate video file size from codec bitrate and recording duration, with presets for common cinema and DSLR codecs. Reverse-calculate the bitrate needed to hit a target file size, and see how many minutes fit on a card or drive. It runs free in your browser on Gera Tools, with nothing uploaded.

Video Bitrate & Storage Calculator

Name: Video Bitrate & Storage Calculator
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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Cinema and high-bitrate codecs eat storage fast, and running out mid-take is expensive. This calculator converts any bitrate and recording length into a file size, reverse-solves the bitrate for a target size, and tells you how many minutes of footage your card or drive will hold.

How it works

Video file size is the simplest media calculation of all — it is just bitrate multiplied by time:

size (megabytes) = bitrate (Mbps) × duration (seconds) ÷ 8

The divide-by-eight converts megabits to megabytes. For a 100 Mbps clip running 60 seconds:

100 × 60 ÷ 8 = 750 MB.

To go the other way and find the bitrate for a target size:

bitrate (Mbps) = (size in MB × 8) ÷ duration (seconds)

Codec presets

The tool loads typical bitrates for common acquisition and delivery codecs:

Codec	Approx. bitrate	Common use
H.264 1080p (streaming)	8–16 Mbps	Delivery / YouTube
H.265 / HEVC 4K	50–100 Mbps	Delivery, efficient 4K
DSLR 4K (8-bit)	100 Mbps	In-camera recording
ProRes 422 LT 4K	~410 Mbps	Editing proxy
ProRes 422 HQ 4K	~880 Mbps	Full-quality post
ProRes 4444 4K	~1320 Mbps	VFX / compositing
Blackmagic RAW 4K (12:1)	~290 Mbps	BRAW acquisition

These are nominal figures at 24–25 fps. Real bitrates vary with frame rate and scene complexity, but they are close enough for storage planning.

Why acquisition and delivery codecs differ so much

Acquisition codecs (ProRes, BRAW, ARRI RAW) prioritize quality and edit-friendliness over compression efficiency. They use intra-frame compression — each frame is stored nearly independently — which makes scrubbing fast and grading easier at the cost of large file sizes. ProRes 422 HQ at 4K runs around 880 Mbps; that is roughly 380 GB per hour.

Delivery codecs (H.264, H.265/HEVC) use inter-frame compression — frames reference each other — to achieve much smaller sizes at similar visual quality. A 1080p H.264 file at 8 Mbps looks excellent on YouTube. The tradeoff is slower rendering and harder scrubbing during editing.

For most workflows: shoot in a high-quality acquisition format, edit with proxies on long projects, and export in H.264 or H.265 for delivery.

How many minutes fit on your card?

The reverse calculation: minutes = (card capacity in MB × 8) ÷ bitrate in Mbps ÷ 60

For example, a 512 GB card (approximately 490,000 MB usable after formatting) shooting ProRes 422 HQ at 880 Mbps:

490,000 × 8 ÷ 880 ÷ 60 ≈ 74 minutes of 4K ProRes 422 HQ.

The same card shooting H.264 at 100 Mbps: 490,000 × 8 ÷ 100 ÷ 60 ≈ 653 minutes.

Notes and tips

Always carry overhead. Cards are sold in decimal gigabytes and the filesystem reserves a few percent, so budget about 10% headroom over the tool’s minutes figure.
Editing codecs are huge — transcode or use proxies for long projects.
Match bitrate to delivery. A 10-minute YouTube upload only needs 16 Mbps H.264; do not shoot in RAW unless you need the grade latitude.

All calculations run locally in your browser.