How Many Hours of Video Per GB

How much video fits in a gigabyte

A gigabyte holds about 16.7 minutes of 1080p video at 8 Mbps, or about 3 minutes of 4K at 45 Mbps. There is no single answer to how many hours fit in a GB, because the file size depends on the bitrate the camera writes at, and that changes with resolution, frame rate and codec.

The arithmetic starts with one fact: a byte is 8 bits, and a gigabyte is 1,000 megabytes in the way storage is sold. One gigabyte is therefore 8,000 megabits. Divide that by the bitrate in megabits per second and you get the number of seconds that fit.

At 8 Mbps: 8,000 / 8 = 1,000 seconds, which is 16.7 minutes. At 45 Mbps: 8,000 / 45 = 177.8 seconds, which is under 3 minutes. The same gigabyte holds 5.6 times less 4K footage than 1080p footage at those rates.

The calculator turns this around and works in hours per card, which is the number that matters when you are packing for a shoot or deciding whether to buy a bigger card.

The formula from bitrate to hours

Video files are described by a bitrate in megabits per second. One hour of video at 1 Mbps is 3,600 megabits, which is 450 megabytes, which is 0.45 GB. So the working rule is simple: gigabytes per hour = bitrate in Mbps x 0.45.

At 8 Mbps that gives 8 x 0.45 = 3.6 GB per hour. At 45 Mbps it gives 45 x 0.45 = 20.25 GB per hour. At 100 Mbps, an 8K or high frame rate setting, it gives 45 GB per hour.

To go the other way, divide the space you have by the gigabytes per hour. A 128 GB card with 7% held back for formatting and the file system leaves 128 x 0.93 = 119.04 GB, and 119.04 / 3.6 = 33.07 hours of 1080p. The same card holds 119.04 / 20.25 = 5.88 hours of 4K at 45 Mbps.

The 0.45 constant assumes decimal gigabytes, which is how storage is sold and how most cameras and computers report file sizes. If a device reports binary gibibytes instead, the same file shows a number about 7% smaller, which is a labeling difference rather than a change in the file.

Worked example: a 128 GB card

Take a 128 GB card, hold back 7% for formatting and the file system, and you have 119.04 GB to fill. At the 8 Mbps that YouTube recommends for 1080p at 30 fps, that is 33.1 hours of footage.

Switch the camera to 4K at 45 Mbps and the same card holds 119.04 / 20.25 = 5.9 hours. Switch to 4K at 60 fps and 66 Mbps and it holds 119.04 / 29.7 = 4.0 hours. Nothing about the card changed; the recording setting did.

A 64 GB card at 1080p holds 64 x 0.93 = 59.52 GB, and 59.52 / 3.6 = 16.5 hours. A 256 GB card at the same setting holds 238.08 / 3.6 = 66.1 hours.

For a two camera interview shoot, budget the number twice. Two 4K cameras at 45 Mbps for a 90 minute session need 2 x 1.5 x 20.25 = 60.75 GB, which fits a 64 GB card only if you stop between takes. A 128 GB card per camera removes the pressure.

Why 4K uses several times the space of 1080p

4K has four times the pixels of 1080p, and camera makers set the bitrate higher than four times to keep the extra detail from turning to mush. That is why the space ratio lands between 4 and 6 rather than at exactly 4.

At the YouTube recommended upload rates, 1080p at 30 fps is 8 Mbps and 4K at 30 fps is 45 Mbps. The ratio is 45 / 8 = 5.625, so an hour of 4K takes 5.6 times the space of an hour of 1080p. At 60 fps the gap widens again, because doubling the frame rate adds roughly 40% to 60% to the bitrate.

Camera bitrates are usually higher than upload bitrates, because the camera records for editing rather than for delivery. A mirrorless camera shooting 4K at 100 Mbps writes 45 GB per hour, which is 2.2 times the 45 Mbps upload rate and fills a 128 GB card in 2.6 hours.

This is the number that catches people on a trip: a card that handled a week of 1080p clips holds an afternoon of 4K.

Bitrates at a glance

The table uses the bitrates YouTube publishes for SDR uploads at standard frame rates, plus two high frame rate settings and one 8K example. Hours are calculated on 128 GB of usable space, which is a 128 GB card after the 7% reserve.

Check one row by hand: 12 Mbps x 0.45 = 5.4 GB per hour, and 119.04 / 5.4 = 22.04 hours. The 256 GB column uses 238.08 GB of usable space, so it is double the 128 GB column in every row.

The bitrates come from the YouTube recommended upload encoding settings, which are a delivery target rather than a recording target. A camera that records at 100 Mbps will always fill a card faster than this table suggests for the same resolution.

Why usable capacity is less than the label

A 128 GB card does not give you 128 GB of files. Two things take a bite before you record a single frame, and they are different problems that people often merge into one.

The first is decimal versus binary. Storage is sold in decimal units, where 1 GB is 1,000,000,000 bytes. Operating systems often report in binary units, where 1 GiB is 1,073,741,824 bytes. Divide 128,000,000,000 by 1,073,741,824 and you get 119.2, which is why a new card shows about 119 GB on a computer. The Apple support note on storage capacity explains the same gap for phones and laptops.

The second is the file system and any reserved space. Formatting writes a directory structure, and cameras and computers keep some room for it, along with a margin so the card does not fill to the last byte. That is the 7% reserve the calculator applies by default, and it is a planning allowance rather than a precise figure.

The terabyte row uses 1,000 GB, the decimal figure on the label, so its planning column is 930 GB. Buy by the number on the label and plan on about 90% of it, then check the first card on a real shoot before you trust the estimate.

What else changes the number

Bitrate is the main lever, but four other things move the answer by enough to matter over a long recording.

Codec. H.265 (HEVC) delivers the same visual quality at roughly half the bitrate of H.264, so a camera set to HEVC fits about twice the footage on the same card. Apple's ProRes and Blackmagic's BRAW go the other way and can be 5 to 10 times larger than H.264 at the same resolution.

Frame rate. Going from 30 to 60 fps adds 40% to 60% to the bitrate in most cameras, not 100%, because the encoder has less time to compress each frame but the frames are more similar.

Audio. A stereo track at 128 kbps adds 0.06 GB per hour, and uncompressed 48 kHz audio adds about 0.7 GB per hour. Small next to video, but not zero on a long interview.

Variable bitrate. Most cameras use VBR, which spends more data on motion and less on a static shot. A talking head video can come in 30% under the nominal rate, and a handheld shot of a crowd can come in over it. Plan with the nominal number and treat the savings as a buffer.

Choosing a card for a shoot

Work backwards from the shoot, not from the card. Estimate the hours you will record, multiply by the GB per hour for your setting, add 20% for retakes and false starts, and then pick the card size that covers it with room for a second camera or a longer day.

A wedding shooter recording 6 hours of 4K at 45 Mbps needs 6 x 20.25 = 121.5 GB, plus 20% is 145.8 GB, so a 256 GB card per camera is the sensible floor. A vlogger recording 30 minutes of 1080p at 8 Mbps needs 0.5 x 3.6 = 1.8 GB, and a 64 GB card covers a week.

Two smaller cards beat one large card for anything paid. A card failure takes the whole shoot with it, and spreading across two 128 GB cards costs the same as one 256 GB card. Dual slot cameras can write to both at once, which is the only real backup during the shoot.

Match the card speed to the bitrate as well. A 100 Mbps recording needs a sustained write of 12.5 MB per second, and a 400 Mbps recording needs 50 MB per second. The V30, V60 and V90 labels on SD cards state the minimum sustained write speed, so a V30 card is rated for 30 MB per second and is comfortable at 100 Mbps but not at 400.

Bitrates and capacities here are planning estimates. Cameras vary in how they encode, cards vary in real world speed, and a card that reports 128 GB may show less once formatted, so test a card before a paid shoot.