What this planner works out
This page holds two calculations. The first estimates storage needs from what a household actually keeps — photos, video and device backups — and adjusts for the protection level chosen. The second projects growth over a planning period with headroom.
Estimating from content rather than from a capacity figure is the more reliable approach, because most people have no idea how much data they have until they add it up.
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Storage Growth Calculator
Estimate future storage needs from your current usage and monthly growth.
Before you buy drives
- The photo estimate assumes about 5 MB per image, which suits phone JPEGs. RAW files are five to ten times that.
- Video is estimated at 8 GB per hour, which is reasonable for 1080p. 4K is several times higher.
- The protection level changes the raw drives needed: a mirror needs twice the data, a parity array around 1.5 times.
- Buy for the planning period, not for today. Adding drives later to an existing array is not always straightforward.
A four-bay NAS filled with small drives has no expansion path — the only upgrade is replacing every drive. Starting with two large drives in a four-bay unit leaves room to add capacity without rebuilding. Drive cost per terabyte falls with size up to a point, and bays are the scarce resource.
How this calculator works
Content summed, then adjusted for protection:
Photos = photos per user × users × 5 MB
Video = hours × 8 GB
Raw data = photos + video + device backups
Drives needed: single 1× raw · mirror 2× · parity array 1.5×The growth calculator on the same page works forward from current data at a monthly growth rate over a planning period, adding headroom. Both figures are worth having — the content estimate says what you need now, the growth figure says what to buy.
Worked example: a household of four
Using the default figures — 4 users with 20,000 photos each, 100 hours of video, 1,000 GB of device backups, no redundancy:
- Photos: 391 GB
- Video: 800 GB
- Total raw data: about 2.14 TB
2.14 TB of actual content. At a mirror that needs 4.3 TB of raw drives; at a parity array around 3.2 TB. Then add growth — at 100 GB a month over three years that is another 3.6 TB — and headroom. A pair of 8 TB drives in a four-bay unit covers it with room to expand, which is a very different shopping list from the 4 TB the raw figure suggests.
Common mistakes
- Buying to today's data. Storage needs only grow.
- Filling every bay at the start. It removes the expansion path.
- Using phone photo sizes for RAW files. They differ by a factor of five or more.
- Forgetting the protection multiplier. A mirror needs twice the raw capacity.
- Treating the NAS as the backup. It is storage; it still needs backing up.
Frequently asked questions
How much storage do I actually need?
Add it up rather than guessing. Photo libraries, video, device backups and document archives are the four main contributors for most households, and the total is usually higher than expected and lower than the capacity people buy. Sizing from measured content plus growth beats sizing from a round number.
Should the NAS be my backup?
It can hold one copy, not all of them. A NAS in the house is vulnerable to fire, theft, flood, a power surge and ransomware reaching it over the network. Three copies of the data, on at least two types of media, with one kept off-site. Each part defeats a different failure: drive failure, accidental deletion, and fire, theft or ransomware. A NAS is an excellent second copy and a poor only copy.
What drives should I use?
Drives rated for continuous operation in multi-drive enclosures — the NAS-specific ranges — rather than desktop drives, which are not designed for constant running or for the vibration of several drives in one chassis. Mixing manufacturers or batches reduces the chance of correlated failure.
How long do NAS drives last?
Published failure statistics suggest most drives run for several years, with failure rates rising after around four to five. Planning to replace drives on a rolling basis before they fail, rather than after, avoids the rebuild risk entirely. Keeping the array's SMART monitoring and scrub schedule active is what makes that possible.
Is what I enter stored?
No. Figures are processed in your browser and never transmitted or retained.
Related tools
References
- National Cyber Security Centre — securing network storage, backup and ransomware resilience
- Information Commissioner's Office — storing personal data securely, including photographs of people
Sources are checked at publication and can change — how I choose and check references.