The amount of storage space a video file takes up is determined by what is known as video bitrate.
A higher bitrate uses more data to encode each second of video, resulting in less compression, higher potential image quality, and larger file size. Conversely, a lower bitrate uses less data to encode each second of video, resulting in more compression, lower image quality, and smaller file size.
The encoding bitrate is determined by your camera’s capabilities and by the settings you use. High-end cameras can encode 4K video at 400 Mb/s or more. Cameras such as action cameras and drones can record 4K video in the 100 Mb/s to 200 Mb/s range. Lower-level or older cameras, such as early-generation 4K cameras, recorded at closer to 60 Mb/s. YouTube recommends a bitrate of between 35 and 68 for 4K videos you upload. 1
Mbps and Mb/s are different ways of writing the same thing. Both refer to megabits per second. They both use a lowercase “b.” Video bitrate is conventionally measured in Mb/s.
If the “B” is capitalized, as in MB/s or MBps, it refers to megabytes per second. There are 8 bits in a byte, so there are 8 megabits in a megabyte. The speed of memory cards is conventionally measured in MB/s.
So there’s a wide range of bitrates that can be used to encode 4K video. And that means there’s a wide range in answering how much 4K video can fit on a 128GB memory card. It can be anywhere from 8 hours to under an hour, depending on the bitrate used. For example, on 128GB, you can fit over 8 hours of 4K footage at a low bitrate of 35 Mbps or about 44 minutes of 4K footage recorded on a high-end camera at 400 Mb/s.
Here’s a table that shows how much 4K video you can fit in 128GB at various bitrates.
4K Video on a 128GB Memory Card Chart
| Video Bitrate (Mbps) | Duration |
|---|---|
| 35 | 8 hours and 19 minutes |
| 45 | 6 hours and 28 minutes |
| 50 | 5 hours and 50 minutes |
| 53 | 5 hours and 30 minutes |
| 60 | 4 hours and 51 minutes |
| 68 | 4 hours and 17 minutes |
| 70 | 4 hours and 10 minutes |
| 78 | 3 hours and 44 minutes |
| 80 | 3 hours and 38 minutes |
| 90 | 3 hours and 14 minutes |
| 100 | 2 hours and 55 minutes |
| 120 | 2 hours and 26 minutes |
| 125 | 2 hours and 20 minutes |
| 150 | 1 hour and 57 minutes |
| 175 | 1 hour and 40 minutes |
| 200 | 1 hour and 27 minutes |
| 230 | 1 hour and 16 minutes |
| 250 | 1 hour and 10 minutes |
| 300 | 58 minutes |
| 320 | 55 minutes |
| 400 | 44 minutes |
4K Video on 128GB Memory Card Calculator
Here’s another option if you need a bitrate that’s not in the chart above.
0 minutes of 4K video footage at
a bitrate of 100 Mb/s.
Does Framerate Affect 4K Video File Size?
Sort of.
Framerate and resolution don’t play direct roles in how much storage space a video file takes up. For instance, 4K30 video encoded at 100 Mbps will take up the same amount of storage space as 4K60 video encoded at 100 Mpbs, which is the same as a 1080p120 file encoded at 100 Mbps.
But they do play indirect roles. And that’s because you get better image quality if you use a higher bitrate when you record at a high framerate. With more frames and higher resolution, there’s more visual information to encode. And so there’s a benefit to using a higher bitrate with those.
So camera manufacturers will often bump up the bitrate along with the framerate. For instance, a camera will usually use a higher bitrate for 1080p240 video than it will for 1080p30. But that’s because of a design choice by the manufacturer to try to keep maximum detail and picture quality in the 1080p240 video by recording it at a higher bitrate. It’s not the framerate directly that’s using more data, it’s the higher bitrate being used to encode video at that framerate setting.
The relationship between framerate and storage size is more direct with high-end codecs such as Apple ProRes and Cineform, where the bitrate, or data rate, is designed to increase along with increasing framerate. That’s where it’s easy to get data rates up over 1900 Mbps, and it’s to do with a different approach to encoding. (You can read a much more technical discussion of how framerate increases data rate in the Apple ProRes codecs in this Apple white paper.) With codecs such as H.264 or HEVC (H.265), which are designed as much for sharing video as for recording, there’s more emphasis on the target bitrate and keeping filesize small. It’s even more direct with RAW capture.
128GB Memory Cards
Here are some fast 128GB memory cards in various form factors.
128GB microSD Cards
- Type: microSDXC
- Video Speed Class: V90
- UHS Speed Class: UHS-II
- Rated read speed: 250 MB/s
- Rated write speed: 130 MB/s
- Type: microSDXC
- Video Speed Class: V30
- UHS Speed Class: UHS-I
- Rated read speed: 200 MB/s
- Rated write speed: 90 MB/s
128GB SD Cards
- Type: SDXC
- Video Speed Class: V90
- UHS Speed Class: UHS-II
- Rated read speed: 300
- Type: SDXC
- Video Speed Class: V90
- UHS Speed Class: UHS-II
- Rated read speed: 300
- Rated write speed: 260
- Type: SDXC
- Video Speed Class: V90
- UHS Speed Class: UHS-II
- Rated read speed: 300
- Rated write speed: 250
128GB CFexpress Type B Cards
- Type: CFexpress Type B
- Rated read speed: 1700
- Rated read speed: 1200
- Type: CFexpress Type B
- Rated read speed: 1750
- Rated read speed: 1000
- Type: CFexpress Type B
- Rated read speed: 1730
- Rated read speed: 1540
Memory Card Tools
Here are a few other related tools I’ve put together that can be useful when working with memory cards and data rates.
Converting Mbps to MB/s & X Speed Rating to MB/s
Another related and common calculation that often needs to be done when working with memory cards is converting the convention for measuring video bitrate (Mbps, Mb/s, or megabits per second) to the convention for measuring the speed of memory cards (MBps, MB/s, or megabytes per second).
So I’ve put together a simple calculator for that separately. You can find it here:
- Convert Megabits Per Second to Megabytes Per Second Calculator
- Convert Memory Card X Speed Rating to MB/s
Memory Card Size Calculators
If you’re trying to figure out what size memory card to buy, it can be useful to know how much video footage from the camera you can fit on a card. Here are a few tools that can be useful for that:
- Video Bitrate vs Memory Card Size Calculator
- How Much 4K Video Can 128GB Hold?
- How Much 4K Video Can 256GB Hold?
- How Much 4K Video Can 64GB Hold?
Working with Memory Cards
Here are some related posts for making sense of memory cards and working with them.
- Fastest SD Card Speed Tests. With cameras getting improved 4K, 5K, and even 8K video recording and burst shooting features all the time, some of them need the write speeds that only the fastest SD cards provide. So here’s a roundup of the fastest SD cards based on my independent tests.
- Fastest MicroSD Card Speed Tests. Need a fast microSD card? If you’re shooting 4K, 5K, or 8K video, high-speed burst-mode photos, or some other demanding use, speed matters. These are the results from my independent speed tests of the fastest microSD cards.
- Types of SD Cards Explained. There are several different types of SD cards, as well as multiple speed rating systems and cryptic codes. Here’s a rundown of what the differences are.
- UHS-I vs UHS-II on microSD & SD Cards. Wondering what the difference is between UHS-I and UHS-II with SD and microSD cards? Here’s an explanation.
- A1 vs A2 SD cards and microSD Cards You might have seen new A1 and A2 speed ratings on some of the newer SD and microSD cards. So what do they mean? And when should you take notice of it?
- SD Card Formatter App for Formatting, Wiping & Repairing SD & microSD Cards. Here’s a guide to using the SD Association’s official SD Card Formatter for preparing your SD and microSD cards for use.
- How to Format SD Cards on Mac. Here’s a step-by-step guide for formatting both SD and microSD cards.
- Best Free Data Recovery Software for SD Cards. Here’s a rundown of the best free data recovery software to use if you’ve accidentally deleted photos or videos from your SD card.
- How to Rover Deleted Photos from SD Card: SD Card Recovery Options. All those photos you took have disappeared from the SD card. The good news is that there’s still a good chance you can recover photos from the SD card. Here’s what to do. Includes free and paid SD card recovery options.
Related Posts
- More specifically, YouTube recommends a bitrate of 35-45 Mb/s for 4K SDR video for footage recorded at framerates of 24, 25, or 30 fps or from 53-68 Mb/s for footage recorded at 48, 50, or 60 fps. For 4K HDR video, they recommend 44-56 Mb/s for standard framerates (24, 25, 30) or 66-85 Mb/s for high framerates (48, 50, 60).[↩]
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