NAS Calculators & Planning Tools
Planning a NAS build or upgrade? These free tools help you calculate real-world usable storage, estimate running costs, and figure out actual transfer speeds, across every major NAS ecosystem. Built on vendor-published data and documented methodology.
Not sure where to start?
- Vendor-published specs and documentation used wherever available, not guesswork
- Where real-world conditions vary (transfer speeds, rebuild times, power use), results show ranges rather than false-precision single numbers
- Override any default with your own figures where prompted for a more precise estimate
Capacity & RAID
Cost & ROI
Performance & Backup
Workload Planning
NBN & Connectivity
Quick Reference
TB to TiB Conversion
| Advertised | Real (TiB) | Shown in OS (GiB, approx) |
|---|---|---|
| 1 TB | 0.909 TiB | ~931 GiB |
| 2 TB | 1.819 TiB | ~1,863 GiB |
| 4 TB | 3.638 TiB | ~3,725 GiB |
| 6 TB | 5.457 TiB | ~5,588 GiB |
| 8 TB | 7.276 TiB | ~7,451 GiB |
| 10 TB | 9.095 TiB | ~9,313 GiB |
| 12 TB | 10.914 TiB | ~11,176 GiB |
| 14 TB | 12.733 TiB | ~13,039 GiB |
| 16 TB | 14.552 TiB | ~14,901 GiB |
| 18 TB | 16.371 TiB | ~16,764 GiB |
| 20 TB | 18.190 TiB | ~18,626 GiB |
| 24 TB | 21.828 TiB | ~22,352 GiB |
Hard drive manufacturers use decimal terabytes (1 TB = 1,000 GB). Many operating systems count in binary units (1 TiB = 1,024 GiB, and 1 GiB = 1,073,741,824 bytes) while still writing "TB" or "GB". So a drive shows 9.05% less in TiB than the TB on its label, or about 6.9% less in GiB. Nothing is missing: it is the same space counted in a bigger unit, before RAID or system overhead.
RAID Level Cheat Sheet
| RAID | Min Drives | Usable Formula | Failures Tolerated | Notes |
|---|---|---|---|---|
| RAID 0 | 2 | n × drive | 0 | Speed only, no redundancy |
| RAID 1 | 2 | 1 × drive | 1 | Mirror, simple, 50% capacity with two drives |
| RAID 5 | 3 | (n−1) × drive | 1 | Survives one drive failure; one drive of capacity goes to parity |
| RAID 6 | 4 | (n−2) × drive | 2 | Survives two drive failures; two drives of capacity go to parity |
| RAID 10 | 4 (even) | (n/2) × drive | 1 (up to 1 per mirror pair) | Speed + redundancy |
| SHR | 1 (2 to survive a drive failure) | Optimised | 1 (with 2 or more drives) | Synology only, uses more of mixed drive sizes |
| SHR-2 | 4 | Optimised | 2 | Synology only |
| RAIDZ1 | 3 | (n−1) × drive | 1 | TrueNAS / ZFS equivalent of RAID 5 |
| RAIDZ2 | 4 | (n−2) × drive | 2 | TrueNAS / ZFS equivalent of RAID 6 |
SHR and SHR-2 minimums are from Synology's own guide, What is Synology Hybrid RAID (SHR)?: "A minimum of four drives is required to create an SHR-2 storage pool that can sustain two drive failures." The formulas assume identical drives and give raw capacity before file system and system overhead. RAID keeps a NAS running through a drive failure; it is not a backup. Not sure which level to choose? The RAID Usable Capacity Calculator compares the space each one leaves you, and the Drive Failure Risk Estimator shows how the risk while a rebuild runs changes between them.
Unraid & ZFS
Try before you buy: official OS demos
Wondering what a NAS operating system looks like? These official vendor demos run the maker's NAS operating system in your browser, with nothing to install and no account of your own. A good way to check whether it suits you before you buy hardware.
How We Calculate
- Where vendor-published data exists (official documentation, knowledge base articles, calculator footnotes), the tool uses it and cites the source.
- Where no published figure exists, the tool labels the value as an estimate or an NTK planning assumption, and where it asks for a figure you can enter your own.
- How each tool works is explained on the tool's own page, in a section such as "How we calculate", not on a separate page.
- No insider claims, no undisclosed vendor relationships, no guesswork presented as fact.
Tool cards and this method last reviewed against each tool: 2026-10-14
Related guides
Frequently Asked Questions
Which tool should I start with?
It depends on your goal. If you're planning a new NAS purchase, start with the NAS Sizing Wizard (how many bays and what drive size) and the RAID Calculator (how much usable space you'll actually get). If transfers feel slow, try the Transfer Speed Estimator to identify your bottleneck. For backup planning, use the Backup Time Calculator alongside the Snapshot Space Estimator. Unraid users have a dedicated set of tools, see the Unraid & ZFS section above.
Why do results differ between NAS brands?
Each NAS operating system implements storage differently. Synology SHR optimises capacity across mixed drive sizes, which gives different usable totals than standard RAID 5 on the same drives. TrueNAS uses ZFS (RAIDZ), which has its own geometry and overhead. Unraid doesn't stripe data, it writes to individual disks, so its effective write speed model is completely different. The calculators account for these differences when you select your platform.
Why do some tools show ranges instead of single numbers?
Where the result depends on conditions nobody can pin down in advance, a single number implies precision that doesn't exist. Real-world transfer speeds depend on file sizes, protocol overhead, NAS CPU, RAM cache, and network congestion. Rebuild times vary with drive activity and controller throughput. Showing a range is more honest, and more useful, because you can see the best and worst case and plan for the realistic middle. Exact arithmetic, such as RAID usable capacity or a TB to TiB conversion, gives an exact figure.
How accurate are these calculators?
The NTKIT tools use vendor-published data wherever available and clearly label any estimated values. Results should be treated as planning estimates, actual capacity, power draw, and transfer speeds depend on your specific hardware, firmware version, and configuration.
Why does my NAS show less space than the drive label says?
Drive manufacturers use decimal terabytes (1 TB = 1,000 GB), but many operating systems count in binary tebibytes (1 TiB = 1,024 GiB). So a "4 TB" drive shows about 3.64 TiB in your NAS, 9.05% less than the label in TiB (about 6.9% less if it is counted in GiB). It is the same space in a bigger unit: this is standard across all brands and is not a defect.
Do these tools work for non-Australian users?
Many of them, yes. The RAID, capacity, rebuild, snapshot, transfer speed, Unraid and ZFS tools use no Australian data. The NAS Power Cost Calculator has electricity rates for Australia by state, the US, the UK, Canada, New Zealand and Europe, or takes the rate from your bill. The other cost tools work in Australian dollars with Australian prices, and the NBN tools cover Australian providers only.
Why do different RAID types give different usable capacity?
Different RAID levels use varying amounts of drive space for redundancy (protection against drive failure). RAID 1 mirrors data across drives (50% capacity), RAID 5 uses one drive's worth for parity, and RAID 6 uses two. The trade-off is always between usable space and how many drive failures you can survive.
Why do you show ranges instead of exact numbers for transfer speeds?
Real-world transfer speeds depend on many factors, network overhead, protocol efficiency, file sizes, NAS CPU, and caching. Showing a range is more honest than a single number. The estimator identifies your primary bottleneck so you know what to upgrade.
Are the Australian electricity rates current?
Each tool that uses them shows the date its Australian electricity rates are from, and the power calculator says when one is due for a re-check. You can always enter the rate from your own electricity bill instead.
Will more tools be added?
Yes. The suite has grown from 12 to 31 tools since launch, adding dedicated Unraid, ZFS, UPS sizing, HDD vs SSD running cost, NAS vs PC cost comparison, drive failure risk, NBN remote access, self-hosted savings, cloud backup time estimation, capacity growth planning, a ranked NAS recommendation tool and an evidence-backed NBN plan finder in early 2026. New tools are added based on the questions we see repeated across the NAS community, check back or subscribe for updates.