Synology Capacity Calculator
Choosing the right storage capacity for a Synology Network Attached Storage (NAS) system can be challenging, especially when you need to balance storage space, data protection, and future expansion. Although adding multiple hard drives increases total storage, not all of that capacity is necessarily available for your files. RAID configurations, Synology Hybrid RAID (SHR), system overhead, and reserved space can reduce the amount of usable storage.
Synology Capacity Calculator
Total Raw Capacity:
Estimated Usable Capacity:
Capacity After Reserve:
Estimated Redundancy:
Estimated Available Space:
Estimates use drive-count-based RAID rules and decimal TB. Actual capacity varies by drive sizes, RAID implementation, filesystem, and system overhead.
The Synology Capacity Calculator helps you estimate how much storage space you can use after selecting your drive count, drive capacity, RAID or SHR configuration, and reserved capacity percentage. It calculates total raw capacity, estimated usable capacity, capacity after reservations, and the equivalent number of drives allocated to redundancy.
Whether you are setting up a home media server, backing up business files, storing photographs, managing virtual machines, or building a NAS for a small office, this calculator can help you plan your storage requirements before purchasing hardware.
The tool supports several common configurations, including SHR, SHR-2, RAID 0, RAID 1, RAID 5, RAID 6, RAID 10, and Basic storage. It also lets you reserve a percentage of capacity for system requirements and snapshots.
The results are estimates based on simplified drive-count calculations. Actual usable capacity can differ depending on drive sizes, RAID implementation, filesystem overhead, and the features supported by your Synology NAS. Use the calculator as a starting point for storage planning, then confirm compatibility and capacity using the specifications for your NAS model.
What Is a Synology Capacity Calculator?
A Synology Capacity Calculator is a storage planning tool that estimates the capacity available in a NAS after accounting for the selected storage configuration and a user-defined reserve.
A NAS is a storage device connected to a network that allows multiple computers, phones, and other devices to access shared files. Synology NAS systems are used for personal backups, media libraries, business documents, surveillance recordings, and other storage-intensive tasks.
When you install multiple drives, the total capacity depends on how those drives are configured. Some configurations combine drive capacities to maximize storage, while others allocate part of the capacity to redundancy.
For example, four 12 TB drives have a combined raw capacity of 48 TB. However, if you use a configuration that reserves the equivalent capacity of one drive for redundancy, the simplified estimate of usable capacity becomes 36 TB before additional reservations.
The calculator helps you understand these differences before committing to a particular drive configuration.
Key Results Explained
The Synology Capacity Calculator provides five main results.
1. Total Raw Capacity
Total raw capacity is the combined advertised capacity of all installed drives.
The formula is:
\[ \text{Raw Capacity}=\text{Drive Count}\times\text{Capacity Per Drive} \]
For example, six 8 TB drives provide:
\[ 6\times8=48\text{ TB} \]
This is the total nominal capacity before accounting for redundancy or other storage overhead.
2. Estimated Usable Capacity
Estimated usable capacity is the amount remaining after applying the calculator's simplified RAID or SHR rules.
Depending on the selected configuration, some drive capacity may be used for redundancy or mirrored data. The remaining capacity can be used to store files, applications, backups, and other information.
3. Capacity After Reserve
The calculator allows you to reserve a percentage of the estimated usable capacity for system requirements, snapshots, or other storage needs.
For example, if the estimated usable capacity is 36 TB and you reserve 10%, the calculation is:
\[ 36\times(1-0.10)=32.4\text{ TB} \]
The estimated capacity after reserve is 32.4 TB.
This is a planning allowance, not a measurement of the exact space consumed by your NAS operating system.
4. Estimated Redundancy
The calculator displays the number of drives' worth of capacity associated with redundancy under its simplified configuration rules.
For example, RAID 5 is represented as having one drive equivalent of redundancy, while RAID 6 is represented as having two.
This figure describes the simplified capacity model. It does not guarantee protection against every hardware failure, data corruption event, or other form of data loss.
5. Estimated Available Space
The calculator displays the capacity after reserve as a percentage of total raw capacity.
The formula is:
\[ \text{Available Percentage}= \frac{\text{Capacity After Reserve}}{\text{Raw Capacity}}\times100 \]
This percentage makes it easier to compare how efficiently different configurations use their nominal storage capacity.
How to Use the Synology Capacity Calculator
Follow these steps to estimate your NAS storage capacity.
Step 1: Enter the Number of Drives
Enter the number of hard drives or storage drives you plan to install.
The calculator accepts between 1 and 100 drives. However, your actual Synology NAS may support far fewer drives, depending on its model, expansion units, and configuration.
For example, enter 4 if you plan to use four drives in your NAS.
Step 2: Enter Capacity Per Drive
Enter the advertised capacity of each drive in terabytes (TB).
Common examples include:
- 4 TB per drive
- 8 TB per drive
- 12 TB per drive
- 16 TB per drive
- 20 TB per drive
If you have four 12 TB drives, the calculator uses 12 TB as the capacity per drive.
The calculator assumes that all drives have the same capacity. If you intend to mix different drive sizes, its results may not accurately represent the storage available under your actual configuration.
Step 3: Select a RAID or SHR Configuration
Choose the storage configuration you intend to use.
The available options are:
- Synology Hybrid RAID (SHR, 1-drive protection)
- Synology Hybrid RAID (SHR-2, 2-drive protection)
- RAID 0
- RAID 1
- RAID 5
- RAID 6
- RAID 10
- Basic
Each option has different capacity and redundancy characteristics. Your NAS model and storage setup must support the selected configuration.
Step 4: Enter the Reserved Capacity Percentage
The calculator defaults to a 10% reserve.
You can adjust this percentage to estimate how much space may remain after setting aside capacity for snapshots, system needs, and other storage requirements.
For example, use 10% for a general planning estimate or test a higher percentage if you expect to maintain substantial snapshots or need additional working space.
The reserve is applied to the estimated usable capacity, not directly to the raw capacity.
Step 5: Click Calculate
Click the Calculate button to view the results.
The calculator displays raw capacity, estimated usable capacity, capacity after reserve, estimated redundancy, and the percentage of raw capacity remaining after the reserve.
Step 6: Compare Different Configurations
Repeat the calculation with different drive counts, drive sizes, or RAID configurations.
This helps you compare storage efficiency and decide whether you need more drives, larger drives, or a different balance between capacity and redundancy.
Use the Reset button to reload the calculator and begin another estimate.
RAID and SHR Configurations Explained
Selecting an appropriate RAID or SHR configuration is one of the most important decisions in NAS storage planning.
Synology Hybrid RAID (SHR)
SHR is designed to simplify storage management and can provide one-drive fault tolerance. Its flexibility with different drive sizes can be useful, but actual capacity depends on the drive combination and supported implementation.
Synology Hybrid RAID 2 (SHR-2)
SHR-2 provides protection against the failure of up to two drives in a supported storage pool. It generally requires at least four drives and sacrifices more capacity to redundancy.
RAID 0
RAID 0 combines drive capacity without redundancy. It can provide high performance in suitable systems, but the failure of a single drive can make the entire array's data inaccessible.
RAID 1
RAID 1 mirrors data across drives. With two equal-sized drives, the simplified usable capacity is equivalent to one drive, while the other provides a mirrored copy.
RAID 5
RAID 5 distributes data and parity across at least three drives. It generally provides capacity equivalent to one drive less than the raw total and can tolerate one drive failure.
RAID 6
RAID 6 uses dual parity and can tolerate up to two drive failures in the array. It requires at least four drives and provides less usable capacity than RAID 5 with the same drive count and sizes.
RAID 10
RAID 10 combines mirroring and striping. It generally requires an even number of at least four drives and provides approximately half of the raw capacity for data, before other overhead.
Basic
Basic storage uses an individual drive without RAID redundancy. It can make the full nominal capacity of the drive available before system overhead, but it does not provide RAID-based protection for that drive.
These descriptions provide a general overview. The actual capacity and supported features depend on the Synology model, drive sizes, and storage configuration.
Formula Used by the Synology Capacity Calculator
The calculator uses simplified capacity formulas for equal-sized drives.
Let:
- \(N\) = Number of drives
- \(S\) = Capacity per drive in TB
- \(R\) = Reserved capacity percentage
- \(U\) = Estimated usable capacity
- \(F\) = Capacity after reserve
Total Raw Capacity
\[ C_{\text{raw}}=N\times S \]
Estimated Usable Capacity
| Configuration | Simplified Formula |
|---|---|
| SHR | \((N-1)\times S\) |
| SHR-2 | \((N-2)\times S\) |
| RAID 0 | \(N\times S\) |
| RAID 1 | \(S\) |
| RAID 5 | \((N-1)\times S\) |
| RAID 6 | \((N-2)\times S\) |
| RAID 10 | \((N/2)\times S\) |
| Basic | \(N\times S\) |
The calculator applies the formulas above to estimate usable capacity. In particular, the RAID 1 formula assumes a simplified mirrored arrangement, while Basic treats the entered drives as separate capacity without redundancy.
Capacity After Reserve
\[ F=U\times\left(1-\frac{R}{100}\right) \]
For example, if usable capacity is 24 TB and the reserve is 10%:
\[ F=24\times0.90=21.6\text{ TB} \]
The calculator estimates 21.6 TB after the reserve.
Available Capacity Percentage
\[ P=\frac{F}{C_{\text{raw}}}\times100 \]
This calculation expresses the capacity after reserve as a percentage of the total nominal drive capacity.
Example: Four 12 TB Drives in a Synology NAS
Suppose you plan to install four 12 TB drives in your NAS and want to compare RAID 5 with RAID 6 using a 10% reserve.
The total raw capacity is:
\[ 4\times12=48\text{ TB} \]
RAID 5 estimate
Raw capacity
48 TB
Usable capacity
36 TB
After 10% reserve
32.4 TB
Drive-failure tolerance
1 drive
RAID 6 estimate
Raw capacity
48 TB
Usable capacity
24 TB
After 10% reserve
21.6 TB
Drive-failure tolerance
2 drives
With these assumptions, RAID 5 provides a larger estimated usable capacity, while RAID 6 provides an additional level of drive-failure tolerance. The appropriate configuration depends on your data, recovery requirements, drive count, and risk tolerance.
These values are simplified estimates. Actual Synology storage pool capacity may be lower after system and filesystem overhead.
Understanding Reserved Capacity and Storage Overhead
The reserved capacity field is useful because a NAS's nominal usable capacity is not necessarily the same as the amount of space available for personal files.
Several factors can affect the space available for everyday use.
System requirements: The NAS operating system and installed applications may use some storage.
Filesystem overhead: Formatting and filesystem metadata can reduce the space available for files.
Snapshots: Snapshots can preserve previous versions of data. Their storage consumption depends on how frequently data changes and how long snapshots are retained.
Shared folders and applications: Files, packages, databases, and virtual machines may require additional working space.
Free-space management: Keeping some space free can help with routine operations, growth, and storage management.
The calculator's reserve percentage is a general planning estimate. It does not automatically determine how much space your system, applications, or snapshots will consume.
For important workloads, monitor actual capacity and set aside a reserve based on your expected usage.
Why Advertised Drive Capacity May Differ From Reported Capacity
Hard drive manufacturers typically advertise capacity using decimal units:
\[ 1\text{ TB}=1,000,000,000,000\text{ bytes} \]
Operating systems and storage utilities may also display capacity using binary units, where one tebibyte (TiB) equals:
\[ 1\text{ TiB}=2^{40}\text{ bytes} \]
Because a tebibyte contains more bytes than a decimal terabyte, a drive advertised as 12 TB may appear as approximately 10.91 TiB before other overhead.
This difference does not necessarily mean that the drive is defective or missing storage. It reflects the distinction between decimal and binary units.
The calculator uses decimal TB for its estimates. Actual displayed values may differ depending on the reporting convention used by your NAS.
Tips for Planning Your Synology NAS Storage
Choose Drives Based on Your Workload
A home media library may require substantial capacity, while a business server may prioritize redundancy, performance, and recovery. Estimate the amount of data you have today and how quickly it is likely to grow.
Leave Room for Future Expansion
If you expect to add photographs, video files, backups, or business records over time, plan for future storage requirements instead of choosing a configuration that will be nearly full immediately.
Check Drive Compatibility
Verify that your selected drives are compatible with your Synology NAS model and the storage configuration you intend to use.
Understand the Difference Between Redundancy and Backup
RAID and SHR can help maintain availability when a supported drive failure occurs, but they do not replace a separate backup. Accidental deletion, malware, theft, fire, and other incidents can affect multiple drives or the entire NAS.
Keep important data backed up to an independent destination, such as an external drive stored separately or another suitable backup system.
Verify the Configuration Before Building
Check the drive count, drive sizes, RAID or SHR requirements, and expected storage pool capacity before purchasing hardware. For mixed-size drives, consult Synology's official capacity tools or documentation because simplified equal-drive calculations may not apply.
Benefits of Using the Synology Capacity Calculator
The calculator can help you make more informed storage decisions.
- Quick capacity estimates: Calculate raw and usable capacity in seconds.
- RAID comparisons: See how different configurations affect storage efficiency.
- Redundancy planning: Understand the simplified capacity cost of protecting against drive failures.
- Reserve planning: Account for a percentage of space that you do not want to allocate to everyday storage.
- Hardware budgeting: Compare different drive counts and capacities before buying drives.
- Storage growth planning: Explore whether a proposed configuration offers enough room for future files and backups.
It is most useful during the planning stage, before you configure your NAS or purchase additional drives.
Frequently Asked Questions (FAQs)
1. What is a Synology Capacity Calculator?
A Synology Capacity Calculator is a tool that estimates the raw capacity, usable capacity, reserved capacity, and approximate redundancy of a NAS based on the drive count, drive size, and selected RAID or SHR configuration.
2. How do I calculate Synology NAS storage capacity?
Multiply the number of drives by the capacity of each drive to determine raw capacity. Then account for the selected RAID or SHR configuration and subtract the chosen reserve percentage from the estimated usable capacity.
3. How much usable space do four 12 TB drives provide?
Four 12 TB drives provide 48 TB of raw capacity. Under the calculator's simplified rules, RAID 5 provides 36 TB before reserve, while RAID 6 provides 24 TB before reserve.
4. What is the difference between raw and usable capacity?
Raw capacity is the combined nominal capacity of all installed drives. Usable capacity is the estimated amount available after accounting for the selected storage configuration and its redundancy requirements.
5. What is Synology SHR?
Synology Hybrid RAID, or SHR, is a storage configuration designed to simplify storage management and provide redundancy. Its capacity and flexibility depend on drive sizes, drive count, and the NAS model.
6. What is the difference between SHR and SHR-2?
SHR typically provides one-drive fault tolerance, while SHR-2 provides two-drive fault tolerance in a supported configuration. SHR-2 generally requires more drives and sacrifices additional capacity for protection.
7. How much capacity does RAID 5 use for redundancy?
For equal-sized drives, RAID 5 generally provides usable capacity equivalent to one fewer drive than the total drive count. For example, four 12 TB drives provide approximately 36 TB before other overhead.
8. How much capacity does RAID 6 provide?
For equal-sized drives, RAID 6 generally provides capacity equivalent to the total capacity of two fewer drives. Four 12 TB drives therefore provide approximately 24 TB before system and filesystem overhead.
9. What is RAID 10, and how much capacity does it provide?
RAID 10 combines mirroring and striping. It generally requires an even number of at least four drives and provides approximately half of the raw capacity for data before additional overhead.
10. What does reserved capacity mean in the calculator?
Reserved capacity is the percentage deducted from estimated usable capacity to account for space you want to leave available for system needs, snapshots, and other storage requirements. The actual amount required depends on your workload.
11. Why does my Synology NAS show less capacity than expected?
Possible reasons include decimal versus binary capacity reporting, RAID or SHR redundancy, system partitions, filesystem overhead, and other storage requirements. Check the capacity units and storage pool details shown by your NAS.
12. Can I use different-sized drives in a Synology NAS?
Some Synology storage configurations support different-sized drives, but the resulting capacity depends on the RAID or SHR implementation and the drive combination. This calculator assumes equal-sized drives, so mixed-drive estimates may be inaccurate.
13. Does RAID protect my files from every type of data loss?
No. RAID can provide protection against certain drive failures, depending on the configuration, but it does not protect against every threat. Maintain separate backups to protect against deletion, malware, theft, and other incidents.
14. How much free space should I leave on my NAS?
The appropriate reserve depends on your applications, snapshots, workload, and future growth. The calculator defaults to 10% as a planning assumption, but you should monitor actual storage use and adjust the reserve to suit your needs.
15. Is the Synology Capacity Calculator accurate?
It provides a useful estimate for equal-sized drives using simplified RAID and SHR formulas. Actual capacity can differ because of model-specific support, drive sizes, implementation details, filesystem overhead, and system requirements. Verify the final configuration with Synology's official tools and documentation.
Conclusion
The Synology Capacity Calculator makes it easier to estimate how much storage you can expect from a NAS before buying drives or configuring a storage pool. By entering your drive count, drive capacity, RAID or SHR configuration, and reserve percentage, you can compare raw capacity, estimated usable space, redundancy, and capacity after reserve.
These estimates can help you plan a home media server, a backup destination, a business file server, or another storage-intensive system. However, the actual result depends on your Synology model, drive combination, storage implementation, and system overhead.
For the best outcome, verify drive compatibility, leave sufficient free space for your workload, and maintain an independent backup of important files. With careful planning, you can choose a storage configuration that better matches your capacity requirements and data protection needs.