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
- Results show ranges, not false-precision single numbers, because real-world conditions vary
- Override any default with your own figures where prompted for a more precise estimate
Capacity & RAID
Cost & ROI
Performance & Backup
Workload Planning
Quick Reference
TB to TiB Conversion
| Advertised | Real (TiB) | Shown in OS (approx) |
|---|---|---|
| 1 TB | 0.909 TiB | ~931 GB |
| 2 TB | 1.819 TiB | ~1,863 GB |
| 4 TB | 3.637 TiB | ~3,726 GB |
| 6 TB | 5.456 TiB | ~5,589 GB |
| 8 TB | 7.275 TiB | ~7,451 GB |
| 10 TB | 9.095 TiB | ~9,314 GB |
| 12 TB | 10.914 TiB | ~11,176 GB |
| 14 TB | 12.733 TiB | ~13,039 GB |
| 16 TB | 14.552 TiB | ~14,902 GB |
| 18 TB | 16.371 TiB | ~16,764 GB |
| 20 TB | 18.190 TiB | ~18,627 GB |
| 24 TB | 21.828 TiB | ~22,352 GB |
Hard drive manufacturers use decimal terabytes (1 TB = 1,000 GB). Operating systems display binary tebibytes (1 TiB = 1,024 GiB). This means every drive shows roughly 6.8% less usable space than the label suggests, 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 |
| RAID 5 | 3 | (n−1) × drive | 1 | Balanced, most common for home NAS |
| RAID 6 | 4 | (n−2) × drive | 2 | Recommended for 4+ bay NAS |
| RAID 10 | 4 (even) | (n/2) × drive | 1 per mirror pair | Speed + redundancy |
| SHR | 2 | Optimised | 1 | Synology only, efficient with mixed drives |
| SHR-2 | 3 | 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 |
Not sure which RAID level to choose? Use the RAID Usable Capacity Calculator to compare configurations with real-world overhead included.
Unraid & ZFS
Try before you buy: official OS demos
Wondering what a NAS operating system actually looks like? These official vendor demos run the real interface in your browser, no account, no download required. A good way to check whether the UI suits you before committing to 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 authoritative figure is available, the tool clearly labels values as "estimated" or "varies by configuration" and offers an Exact Mode for users to enter their own numbers.
- Formulas and assumptions are documented on each tool's "How it works" page. The NTKIT editorial team reviews and updates these regularly.
- No insider claims, no undisclosed vendor relationships, no guesswork presented as fact.
Last reviewed: 20 March 2026
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 you show ranges instead of single numbers?
Single numbers imply 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.
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 operating systems display binary tebibytes (1 TiB = 1,024 GiB). This means a "4 TB" drive shows approximately 3.64 TiB in your NAS, about 6.8% less than the label. This is standard across all brands and is not a defect.
Do these tools work for non-Australian users?
The RAID calculator and transfer speed estimator work for any user worldwide. The power cost calculator defaults to Australian electricity rates but allows custom rate input, so it works internationally too.
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?
Rate defaults are based on publicly available average residential tariffs by state. They are reviewed periodically and users can always enter their own rate from their electricity bill for the most accurate estimate.
Will more tools be added?
Yes. The suite has grown from 12 to 29 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, and capacity growth planning tools in early 2026. New tools are added based on the questions we see repeated across the NAS community, check back or subscribe for updates.