Video file size calculator

Every recording format has a data rate, and the data rate decides nearly everything else about storage: how many cards to pack, how big the drives must be, how long the offload takes at the end of a long day. The video file size calculator converts a bitrate into gigabytes and then scales it up to a whole shoot.

How the video file size calculator works

Bitrates are given in megabits per second (Mb/s). A byte is 8 bits, and the tool counts the way card and drive makers do: 1 GB = 1,000,000,000 bytes.

• Gigabytes = Mb/s × 1,000,000 × seconds ÷ 8 ÷ 1,000,000,000. For one hour that comes down to Mb/s × 0.45.
• Per shoot day is the gigabytes for your recorded minutes. The whole shoot is that figure times the number of days.
• With two backup copies is the whole shoot × 2: the drive space you need when every card is copied to two drives.
• Recording time on a card = card size × 0.95 × 8,000 ÷ Mb/s ÷ 60, in minutes. The tool keeps 5 per cent of each card free for the file system and a safety margin.

The menu holds seven ProRes options (422 HQ, 422 and LT at UHD; 422 HQ, 422, LT and Proxy at HD), all at the target rates for 24p published in Apple's ProRes white paper, plus long-GOP camera codecs at 200, 100 and 50 Mb/s. Choose "Another bitrate" to type your own.

Worked example: ProRes 422 HQ in HD, a five-day shoot

The tool opens with ProRes 422 HQ, HD 1920 x 1080, 24p, which Apple publishes at a target rate of 176 Mb/s. It assumes 120 recorded minutes a day, 5 shoot days and a 256 GB card, and reads:

• Per hour of recording: 79.2 GB
• Per shoot day: 158.4 GB
• Whole shoot, camera originals: 792 GB (0.79 TB)
• With two backup copies: 1.58 TB of drive space
• Recording time on a 256 GB card: about 184 minutes

The sums are short. 176 × 0.45 = 79.2 GB an hour, and two hours a day makes 158.4 GB. Five days come to 792 GB of camera originals, and two copies of that need 1,584 GB, or 1.58 TB. For the card, 95 per cent of 256 GB is 243.2 GB, which holds 184 minutes at 176 Mb/s. The preview shows a day of footage filling 62 per cent of a card, so one card covers a day here with room to spare. Switch to ProRes 422 HQ at UHD, 707 Mb/s, and the same card holds about 46 minutes.

A simple kit for those numbers is a card in the camera, a portable SSD for the first copy and a larger hard drive for the second: the 2 TB SSD takes one 792 GB copy and the 5 TB drive takes the other. We chose the three items below from published specifications and long-standing reputations; they were not tested by us.

Card speed matters as much as size. A V30 card is rated to write at least 30 megabytes a second, which is 240 Mb/s: enough for the long-GOP rates in the menu, nowhere near UHD ProRes. Your camera's manual lists the cards it accepts for each mode.

ProRes data rates and camera codecs

ProRes rates rise in step with frame rate. Apple lists HD ProRes 422 HQ at 220 Mb/s for 30p and 440 Mb/s for 60p, so for anything faster than 24p, type the published figure for your rate into "Another bitrate". Long-GOP figures are the numbers in a camera's menu, and they work as ceilings: real files can come in under them.

How much storage for 4K?

The codec decides far more than the resolution. UHD ProRes 422 HQ at 24p fills 318.2 GB an hour. A long-GOP file at 100 Mb/s, a common UHD setting on mirrorless cameras, fills 45 GB. Same frame size, seven times the storage. Type 1000 into the card size box and the tool shows about 179 minutes of the ProRes on a 1 TB drive, against about 1,267 minutes of the 100 Mb/s file.

Scale matters too. A feature documentary can come home with 200 hours of material, the figure our editing guide works from; at 79.2 GB an hour that is 15.8 TB before a single backup.

The 3-2-1 backup rule

Keep three copies, on two kinds of media, with one copy somewhere else. The tool's two backup copies plus the camera card make three, but only until the card is formatted for reuse. Make a third copy before you wipe it (another drive, or an upload), or keep cards untouched until both copies are checked. On the road, the two drives travel in different bags.

What the calculator cannot tell you

ProRes rates are targets, and detailed or noisy pictures run above them, so leave a margin. The menu rates cover picture only; files from a separate sound recorder need their own room (two tracks of 48 kHz, 24-bit audio add about 2.3 Mb/s). The tool does not count proxies, render files or exports in the edit, and it does not check whether a card is fast enough. The rest of the Kit Room covers framing, shutter and timecode.

Questions

How do I work out video file size from bitrate?

Multiply the bitrate in Mb/s by the seconds recorded, divide by 8 for megabytes, then by 1,000 for gigabytes. For one hour, Mb/s × 0.45 gives gigabytes, so 176 Mb/s is 79.2 GB an hour.

How much storage do I need for an hour of 4K?

From the formats in the tool, between 45 GB for a 100 Mb/s long-GOP file and 318.2 GB for UHD ProRes 422 HQ at 24p. The codec makes the difference.

How long will a 256 GB card record?

About 184 minutes at 176 Mb/s, keeping 5 per cent of the card free. At 707 Mb/s it is about 46 minutes, at 100 Mb/s about 324.

Why does my computer show less space than the card label?

Card makers count 1 GB as 1,000,000,000 bytes, as this tool does. Software that counts in binary units, where one unit is 1,073,741,824 bytes, shows a 256 GB card as about 238.