Top 3 picks at a glance
The Short Answer
For most households, start with 4TB to 8TB of usable NAS storage if you are backing up 2 to 3 computers, phones, and a modest photo library. A good rule of thumb is to buy 2x to 3x your current data footprint. Add up what you have today, double it for version history and growth, then add overhead for RAID protection.
Here is a quick way to estimate: Total current data across all devices x 2.5 = usable terabytes you should target. If you have 2TB of data today, aim for 6TB usable. If you have 4TB today, aim for 10TB to 12TB usable. Because RAID 1 and RAID 5 reserve one or more drives for redundancy, your raw capacity needs to be larger than your usable capacity. As of 2026, with 4K video, larger phone backups, and growing media libraries, most buyers are best served by a 2-bay or 4-bay NAS populated with 4TB to 8TB drives per bay.
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Standard Sizes
NAS devices are sized by bay count and drive capacity, not just terabytes. The physical footprint, weight, and power draw matter if the unit will sit on a desk, in a closet, or on a media console. The table below shows common desktop NAS sizes you will actually find at retail, with real-world dimensions, weights, and typical street prices.
| Form Factor | Typical Raw Capacity | Usable Capacity (with RAID) | Dimensions (inches / cm) | Weight (with drives) | Typical Power Draw | Typical Price Range |
|---|---|---|---|---|---|---|
| 2-Bay Desktop (e.g., BUFFALO LinkStation 720 8TB) | 4TB to 16TB (2x 2TB to 8TB drives) | 2TB to 8TB in RAID 1 (mirrored) | 3.4 x 5.0 x 8.0 in / 8.6 x 12.7 x 20.3 cm | 4.5 to 5.5 lb / 2.0 to 2.5 kg | 18W to 36W active, 8W to 12W idle | $300 to $500 |
| 4-Bay Desktop (e.g., BUFFALO TeraStation Essentials 4-Bay 8TB) | 8TB to 64TB (4x 2TB to 16TB drives) | 6TB to 48TB in RAID 5 | 6.7 x 6.8 x 9.1 in / 17.0 x 17.3 x 23.0 cm | 14 to 18 lb / 6.4 to 8.2 kg | 35W to 65W active | $600 to $900 |
| 8-Bay Desktop Tower (e.g., QNAP TS-832PX-4G) | 16TB to 128TB (8x 2TB to 16TB drives, diskless or populated) | 14TB to 112TB in RAID 6 | 7.3 x 11.7 x 9.7 in / 18.5 x 29.8 x 24.6 cm | 19 to 22 lb without drives / 8.6 to 10 kg; 28 to 35 lb loaded | 45W to 90W active | $850 to $1,150 diskless, $1,600+ populated |
| Single Enterprise Drive (e.g., Toshiba MG08ACA16TE 16TB 3.5″ HDD) | 16TB per drive | N/A (used inside NAS) | 5.8 x 4.0 x 1.0 in / 14.7 x 10.2 x 2.6 cm | 1.6 lb / 0.72 kg | 7W to 10W per drive active | $250 to $450 per drive (renewed vs. new) |
Capacity math to remember: In a 2-bay NAS with RAID 1, usable space equals one drive. Two 8TB drives give you 8TB usable. In a 4-bay NAS with RAID 5, usable space equals three drives. Four 4TB drives give you 12TB usable, four 8TB drives give you 24TB usable. For an 8-bay NAS with RAID 6, usable space equals six drives. Eight 8TB drives give you 48TB usable.
How to Measure Your Space
NAS sizing is not just about terabytes. You need to make sure the box physically fits, ventilates, and can stay connected to power and your router. Measure before you buy.
- Measure the footprint. Use a tape measure to record the width and depth of the shelf, desk, or media console. Add 2 inches / 5 cm of clearance on each side and 4 inches / 10 cm behind for cables and airflow. A 2-bay unit needs about 8 x 10 inches / 20 x 25 cm of clear surface. A 4-bay needs about 10 x 12 inches / 25 x 30 cm. An 8-bay tower needs about 12 x 14 inches / 30 x 36 cm.
- Measure vertical clearance. Include feet and any top vent. You need at least 2 inches / 5 cm above the NAS for heat exhaust. Enclosed cabinets trap heat. If the cabinet has a door, you must have a vent or leave the door open during heavy backup jobs.
- Check ventilation path. Most desktop NAS units pull air front-to-back or front-to-top. Confirm there is open air at the front intake and rear exhaust. Do not push the NAS flush against a wall. Leave 3 to 4 inches / 7.5 to 10 cm behind it.
- Map cables and power. Measure the distance to your router or switch for Ethernet. For reliable backups, use a wired connection. Cat5e or Cat6 cable runs over 150 feet / 45 meters can affect speed and should be avoided. Also confirm you have a dedicated outlet. Use a surge protector or UPS. A 2-bay uses 18W to 36W, a 4-bay uses 35W to 65W, so a compact 600VA UPS will handle a short outage.
- Check noise and floor stability. A loaded 4-bay or 8-bay NAS produces 20 to 28 dB at idle and higher with drive activity. Place it on a solid, level surface away from bedrooms if you are noise sensitive. Avoid soft fabric surfaces that block bottom vents.
- Plan for drive access. You will need to slide drives in and out. Ensure there is 6 to 8 inches / 15 to 20 cm of clear space in front of the bays for hot-swap trays. For rack or closet installs, pull the unit fully out before removing drives.
By Room or Use Case
Home Office or Small Apartment: 4TB to 8TB Usable
Best for: 1 to 2 computers, phone photo backups, and documents. If your combined data is under 1.5TB today, a 2-bay NAS with two 4TB drives in RAID 1 gives you 4TB usable. That covers a full system backup for each computer plus 12 to 18 months of Apple Time Machine or Windows File History versions. It fits easily on a desk at roughly 3.5 x 5 x 8 inches and stays quiet and efficient at under 30W. If your data is closer to 2.5TB, move to two 8TB drives for 8TB usable. Price expectation is $300 to $500 for a populated 2-bay like the BUFFALO LinkStation 720 8TB, which typically streets around $417.99.
Family Household with Photos and Video: 8TB to 16TB Usable
Best for: 3 to 5 users, shared photo library, iCloud or Google Photos archive, and light media streaming. Families often have 3TB to 6TB of real data once you count RAW photos, 4K phone video, and multiple user folders. Plan for 12TB to 16TB usable to allow for growth and versioning. A 4-bay NAS with four 4TB drives in RAID 5 yields 12TB usable and tolerates one drive failure. Four 6TB drives yield 18TB usable. This setup needs about 7 x 7 x 9 inches of shelf space and weighs 14 to 18 pounds loaded, so place it on a lower shelf or sturdy console. Budget $600 to $900 populated, with value 4-bay kits like an 8TB (4x2TB) configuration streeting near $727.99 before upgrades.
Creator, Photographer, or Home Media Server: 16TB to 36TB Usable
Best for: 4K video editing archives, Lightroom catalogs, Plex or Jellyfin libraries, and weekly full backups. Creators should add up active projects plus archive. A single hour of 4K 30fps footage can be 40GB to 100GB depending on codec. If you keep 10TB to 15TB of active and archived media, aim for 24TB to 36TB usable. A 4-bay with four 12TB drives in RAID 5 gives 36TB usable. An 8-bay lets you start with six 8TB drives in RAID 6 for about 32TB usable and expand later. Enterprise-class drives such as the Toshiba MG08ACA16TE 16TB run at 7200 RPM and are built for 24/7 NAS duty, with street prices from $250 for renewed units to $434 and up new. Allow 45W to 70W power draw and ensure wired Gigabit Ethernet or faster for smooth 4K streaming.
Small Business or Power User: 32TB to 72TB Usable
Best for: 5 to 15 users, daily incremental backups, surveillance footage, or virtual machine images. Businesses need more redundancy and retention. Choose an 8-bay unit like the QNAP TS-832PX-4G, priced near $999 diskless, and populate with NAS-rated drives. Eight 8TB drives in RAID 6 give 48TB usable with two-drive fault tolerance. Eight 12TB drives give 72TB usable. If you must retain 30 days of daily version history and 12 monthly snapshots, multiply your weekly change rate by retention length. For example, 500GB of weekly change x 12 weeks = 6TB just for versions. Always keep the NAS on a UPS and replicate critical data offsite or to a second NAS.
Common Sizing Mistakes
1. Buying for today, not for three years. Data typically grows 20 to 40 percent per year. A unit that fits exactly today will be full in 12 months. Add at least 50 percent headroom beyond your current total, and choose a 4-bay if you can only afford small drives now. It is far cheaper to add drives than to migrate to a new NAS.
2. Forgetting RAID overhead. Shoppers see 8TB raw on the box and assume 8TB usable. In RAID 1, you lose half. In RAID 5, you lose one drive. Calculate usable first. If you need 8TB usable, you must buy 16TB raw for a 2-bay or 12TB raw for a 4-bay.
3. Ignoring version history. Backup software keeps multiple versions of changed files. That safety net costs space. Time Machine and similar tools can easily consume 1.5x to 2x your primary drive size over time. If you back up a 1TB laptop with daily changes, budget 1.5TB to 2TB for its backup chain alone.
4. Mixing drive sizes incorrectly. Using mismatched drive capacities in traditional RAID wastes space. Three 4TB drives plus one 8TB drive in RAID 5 still only yields 12TB usable, wasting 4TB on the larger drive. Buy matched drives per array, and use expansion units or storage pools if you must mix.
5. Putting the NAS where it cannot breathe or connect. A closet with no ventilation will throttle performance and shorten drive life. A Wi-Fi-only connection will make initial backups painfully slow. Place the NAS near your router, use Ethernet, and keep it dust-free with front-panel filters cleaned every 3 to 6 months.
FAQ
How do I calculate how many terabytes I need for NAS backup?
Add up the used space on every device you plan to back up. Include external drives, phone backups, and any media library you will archive on the NAS. Multiply that total by 2 to account for versioning and near-term growth. Then factor RAID. For a 2-bay in RAID 1, divide your usable target by 1 to get drive size. For a 4-bay in RAID 5, divide by 3. Example: You have 3TB total today. 3TB x 2.5 = 7.5TB usable needed. A 2-bay would need two 8TB drives, a 4-bay would need four 4TB drives for 12TB usable.
Should I use RAID 1, RAID 5, or RAID 6?
RAID is not a backup by itself, it is uptime protection against drive failure. Use RAID 1 for 2-bay units. Use RAID 5 for 4-bay to 6-bay units where one drive of fault tolerance is acceptable. Use RAID 6 for 8-bay and larger where you want two drives of fault tolerance and longer rebuild times. For any RAID 5 or 6 setup, keep a cold spare drive or enable hot spare if your model supports it so rebuilds start quickly.
Can I start small and add larger drives later?
Yes, but plan for it. Many modern NAS systems support online capacity expansion and storage pools that let you replace drives one at a time with larger ones and then expand the volume. With traditional RAID, you must replace all drives in the array before you see more usable space. Also remember that initial backups of 2TB to 6TB can take 8 to 24 hours even over Gigabit Ethernet, so schedule the first run overnight and keep the NAS wired.
How long will a given NAS size last before it is full?
Take your usable capacity and subtract current data, then divide by your annual growth. If you buy 12TB usable and have 5TB today with 1TB of yearly growth, you have about 7 years of headroom. With heavier photo and video growth of 2TB per year, the same 12TB gives you about 3.5 years. If you archive media rather than delete it, assume the higher growth rate and choose the next size up.
