How Much Storage Do You Need for Blu-ray Backups?

To work out how much storage your Blu-ray rips need, measure representative files from your own collection, then budget each storage destination separately. Include the versions you will retain, expected growth, free-space allowance, and any extra workspace on that destination. A disc count alone cannot tell you which drive to buy.

This worksheet is for self-authored or authorized media your tools can already read. It plans capacity; it does not explain bypassing copy protection or promise that a particular NAS will play your files.

Decide what you are actually keeping

Make one row per kind of retained output. A full-disc archive and a separate smaller playback file both occupy space if you keep both. Do not count an MKV and an ISO as two retained versions if you intend to keep only one.

Keep different source types and output settings in separate groups. Record extras and audio/subtitle selections before measuring; changing what you retain changes the budget. If the output choice is still unclear, use Copy vs Ripper first.

The Blu-ray Disc Association lists ordinary single- and dual-layer capacity as 25 GB and 50 GB. Those are disc capacities, not measured file sizes or a range covering every UHD/BDXL format. Measure the actual output you intend to retain.

Use complete samples, not a promised compression percentage

Start with a few representative items in each group, including a longer or more complex example. Record the mean, the largest result, and the settings. A small sample gives a provisional budget, not a statistical guarantee; compare the first completed batch with the estimate and revise it.

Run the worksheet once with each group’s mean and again with its largest measured sample. The second result tests a larger-file scenario; it is not an upper bound for items you have not processed. If that scenario no longer fits, gather more samples or revise the capacity plan before committing.

For re-encoded copies, a short preview helps assess quality but cannot reliably predict the size of an entire title. HandBrake explains that constant-quality output size varies with the source. Its technical page is marked as a draft. Do not budget on an assumed fixed reduction from ISO to MKV or MP4. See the MP4 workflow for checking a playback copy before committing to it.

Calculate the retained collection

For each group, multiply the item count by your measured mean size. Add the groups and any additional versions you will keep. Store raw byte counts when possible so every row uses the same unit.

The following numbers are invented only to demonstrate the arithmetic. They are not typical Blu-ray sizes or results from our tests. All GB here are decimal.

If you choose not to retain the extra playback copies, this example becomes 1,640 GB. That is a change in the retained set, not an improvement in compression.

Budget each destination, including growth

Suppose you plan to add another 500 GB before your next review and choose to keep 20% of the usable volume empty. That percentage is an example of a planning choice, not a universal storage requirement.

Planned retained data = 2,000 + 500 = 2,500 GB
Usable volume needed = 2,500 / (1 - 0.20) = 3,125 GB

Multiplying 2,500 by 1.20 gives 3,000 GB, which leaves only 500/3,000, or about 16.7%, empty. Use division when the target is a fraction of the final volume.

For a separate backup containing the same planned set, budget 3,125 GB of usable volume there too. If its contents or retention history differ, calculate that destination again. Do not assume compression or deduplication will save space before measuring the actual backup.

The Library of Congress recommends copies on different media in separate physical locations. Two drives inside one mirrored array do not provide that separate-location copy. Decide what each independent destination must recover using the personal archiving guide.

Add workspace only where the job needs it

An encode or ISO creation job may need the readable source, destination output, and temporary files to coexist. Check which volume holds each one. Count only the additional space not already included in that volume’s retained-data total; otherwise you may count a source or output twice.

If the working volume in the example also needs 200 GB of additional concurrent workspace, the same 20% free-space target gives:

Working volume = (2,500 + 200) / 0.80 = 3,375 GB usable
Independent backup without that workspace = 3,125 GB usable

The 200 GB is another hypothetical input, not a software requirement. Check your tool’s estimate and observe a representative job. Multiple simultaneous jobs can need overlapping workspace. If temporary files live on another drive, check that drive separately. Recheck free space immediately before a batch; a long-term capacity plan is not evidence that today’s job fits.

Compare usable capacity in matching units

NIST distinguishes 1 GB = 1,000,000,000 bytes from 1 GiB = 1,073,741,824 bytes. A different display unit does not mean files have disappeared. Record whether your measurements and storage estimate use decimal GB/TB or binary GiB/TiB before comparing them.

The numbers above are requirements for usable volume capacity, not a recommendation to buy drives with that combined label capacity. RAID layout, system partitions, filesystem metadata, existing files, and backup versions also matter. Synology’s RAID calculator notes explicitly distinguish its estimate from actual volume capacity. Confirm the result in the storage manager for your real configuration.

Before buying or processing the full collection, check that:

• Your samples include the tracks and extra versions you plan to retain.
• Each destination has its own file set, growth period, and free-space calculation.
• Temporary space is assigned to the correct volume without double-counting.
• Units and usable capacity match; raw drive totals are not treated as independent backups.
• A representative output opens correctly and a backup can be restored before the source is discarded.

This is a documented planning method with checked arithmetic. We have not measured your collection or tested discs, storage hardware, NAS playback, or compression performance for this guide.