If you’re going to purchase Blu-ray movie discs from some small shops, or want to buy some blank Blu-ray discs on behalf of video burning or data storage, you must get to learn some basic knowledge about Blu-ray disc size. Why is it important? Because Blu-rays are in different sizes. If you bought a Blu-ray to burn data that larger than its capacity, let’s say – 40GB of data on a BD-25, this would not work.
In this post, we explain about BD-25, BD-50, BD-66, BD-100, BD-128, BD-XL, 4K UHD BD-ROM, BD-5, BD-9, etc. BD-5 and BD-9 usually involve “fake Blu-ray“, which you should really be careful whenever buying cheap Blu-ray movie discs.
BD-25 and BD-50 are the Two Most Familiar Blu-ray Disc Size
The most commonly sell blank Blu-ray discs on online shopping sites are BD-R 25GB or BD-R 50GB. They are usually sold in bundle pack of 10 pieces, 25 pieces, 50 pieces, 100 pieces, etc. BD-R (Blu-ray Recordable) means that the blank Blu-ray disc can only be written ONCE. If you have burnt a BD-R but found ‘oops! I just burnt something wrong’, well, this BD-R disc can still be used as a coaster.
Nor does it mean that there is no blank Blu-ray disc that can be rewritten, that kind of disc is called BD-RE, which means Blu-ray REwritable. Similar to BD-R, BD-RE discs also have different capacities like BD-RE 25GB, BD-RE 50GB, BD-RE 100GB, etc. The price of a 25GB BD-RE disc is usually more than twice that of a 25GB BD-R.
Key Point #1. “BD-25” or “BD-50” are the collective names of the Blu-ray discs with a maximum size of 25GB or 50GB. The word BD-25/50 may refer to BD-R 25GB/50GB, BD-RE 25GB/50GB, or the pre-recorded movie disc BD-ROM (Read Only) 25GB/50GB.
| Blu-ray Disc Type | Capacity | It Is Called… |
| BD-R | 25GB | BD-25, BD-R 25GB, BD-R SL, BD-R Single Layer |
| 50GB | BD-50, BD-R 50GB, BD-R DL, BD-R Dual Layer | |
| BD-RE | 25GB | BD-25, BD-RE 25GB, BD-RE SL, BD-RE Single Layer |
| 50GB | BD-50, BD-RE 50GB, BD-RE DL, BD-RE Dual Layer |
As the above table show, BD-50 has another designation and it’s called dual-layer Blu-ray. A BD-25 disc is called single-layer Blu-ray, although we rarely call it that.
‘Dual-layer’ means the Blu-ray disc has double layers for offering twice the storage capacity of a Blu-ray 25 gigabytes disc. With this advantage, the movie publishers can add more behind-the-scenes videos, interactive media, unique movie clips, and high-resolution audio choices to the Blu-ray disc. The main movie might also have better encoding. The first dual-layer BD-ROM movie discs were introduced in 2006, a comedy ‘Click’ starring Adam Sandler.
By the way, BD-50 is the minimum capacity standard for 4K UHD Blu-ray movies. Normal Blu-ray players can read 1080P BD-50 discs, but not the commercial BD-ROM 50GB discs at 4K (2160P) resolution.
Key Point #2. Due to differences in calculation methods, the capacity of BD-25 on Windows computers will be displayed as about 23GB, and BD-50 on Windows computers will be displayed as about 46GB, which means you can only burn about 23GB or 46GB to the disc.
High-capacity Blu-rays: BDXL 100/128 GB
Have you taken a look at the BDXL disc? The physical structure of BDXL is at least triple layers. BDXL means Blu-ray Disc EXtra Large.
| Layers | Disc Size | R | RE |
| Triple BDXL | BD-100 | ✔ | ✔ |
| Quad BDXL | BD-128 | ✔ |
Many people would also ask how many GB a 4K BD-ROM movie is. There are three types actually: 50GB, 66GB, and 100GB. The first commercially available 100GB 4K UltraHD Blu-ray disc was ‘Batman v Superman’ retailed in 2016.
The birth of BD-100 UHD Blu-ray allows more munificent bitrates. BD-50 at 82Mbit/s. BD-66 at 108Mbit/s. BD-100? 128Mbit/s.
And here is some important information if you’re going to purchase an external Blu-ray drive or Blu-ray player. Some 4K UHD Blu-ray drives (shall support BD-ROM 50GB, 66GB, 100GB) also can read and write both BDXL 100GB & 128GB. You can usually see the BDXL logo on the shell or find relevant content in the user manual. The BDXL drive without the 4K UHD logo will definitely not be able to play 4K UHD Blu-ray discs, though 1080P BDXL-R or BDXL-RE movies are supported.
People in the forum have made some interesting attempts to test whether a normal 4K UHD Blu-ray player can read the BDXL-100 that the content does not exceed approx 66GB (a triple disc but the data was written only to the first two layers). Some players have been confirmed as YES (e.g. Sony UBP-X700). Good to know we are able to full copy a commercial BD-ROM 66GB to a 100GB blank BDXL disc and enjoy it on some 4K Blu-ray players.
Blu-ray is moving towards bigger capacity. Won’t be surprised if next-gen optical discs are BD 200GB, BD 300GB, BD 500GB, etc.
[Blu-ray on DVD] BD-5 and BD-9
Many years ago when Blu-ray movie discs first came out, people were showing great interest. Some vendors or small shops pirated Blu-ray discs and sold at a much cheaper price. When the customer took it home and played, they might find the quality was just horrible. The video resolution might be 1080P or 720P, but the whole video was bad. It just didn’t look like Blu-ray.
These poor-quality pirated copies are usually BD-9. They are not even real Blu-ray but DVD disc. The vendors copy the whole Blu-ray movie to a DVD-9, and because the Blu-ray file structure is retained, the disc is called “BD-9”. Since BD-5 has 4.7GB of capacity and BD-9 has 8.5GB of capacity, the bitrate must drop hard, even if the disc is in 1080P/720P resolution.
It should be clear now that both BD-5 and BD-9 are the type of disc that use DVD disc as the medium but store videos in Blu-ray structure. BD-5 and BD-9 are only playable on Blu-ray players.
From the perspective of personal use, the characteristics of BD-5 and BD-9 discs also make it very easy for individuals to burn high-quality videos at a lower cost. As long as the video itself is not long (usually less than 1 hour), you can burn HD video to BD-5/BD-9 without losing any quality. What you need is a standard blank DVD disc.
The explanation of BD-25, BD-50, BD-66, BD-100, BD-128, BD-5, BD-9 are all here. The basic knowledge will be helpful to make your own decision when buying Blu-ray disc, Blu-ray drive, or Blu-ray player.