Quick answer
This technical calculator uses visible units and deterministic formulas to estimate capacity, transfer time, latency, or hardware planning values.
Best for: comparing realistic scenarios before acting. Not for: final professional guidance, emergency decisions, or replacing product labels and local requirements.
How to use the calculator
- Enter the measurements, quantities, costs, or target values requested above.
- Adjust optional assumptions such as waste, overhead, product strength, retention days, or multipliers.
- Read both the main result cards and any warning notes. The warnings are part of the answer, not fine print.
- Use the share, copy, or print/PDF controls when you want to save the scenario.
What the results mean
The primary result is the main number to use first. Supporting cards show the inputs, ranges, assumptions, or follow-up checks that explain how to interpret it.
Decision notes for this calculator
Use: Planning aid
The labeled inputs and visible assumptions shown in the form move the result most.
Sources and assumptions
Use the inputs, units, and assumptions shown on the page, then compare important results with product documentation, vendor guidance, local code, or a qualified professional when the decision has safety or cost consequences.
- NIST binary prefixes and SI units
- SNIA Dictionary for storage terminology
- CalculatorShelf source guide: storage formulas
Method version: WINDOWS_STORAGE_SPACES-1.0. Send corrections through the contact page.
What to do next
Compare a conservative scenario with your real requirements before acting.
Save this scenario
Use Share to copy a clean URL with your inputs, Copy result for notes or email, and Print / PDF for a saved scenario. If the result looks wrong, report an issue with the Windows Storage Spaces Calculator.
Formula / methodology
Usable capacity is modeled from drive count × drive size divided by the selected resiliency rule: two-way mirror ≈ 50%, three-way mirror ≈ one-third, parity ≈ (drives − 1) drives before layout details.
Assumptions and limitations
- Inputs are assumed to be measured accurately and entered in the units shown.
- Rounding is intentional so the result is easier to use in real decisions.
- Vendor-specific behavior, local code, product labels, and regional pricing can override a generic calculator.
- Health, legal, tax, emergency, structural, chemical, and other high-risk decisions need qualified guidance beyond a web calculator.
Example calculation
Input: four 10 TB drives in two-way mirror. Raw capacity is 40 TB and planning usable capacity is about 20 TB before filesystem and pool overhead.
Common mistakes
- Using rough inputs when the estimate depends on exact measurements.
- Ignoring waste, overhead, local prices, or product-specific instructions.
- Treating an early estimate as a final quote or professional guidance.
- Comparing results without checking units and assumptions.
FAQ
What formula does this page use?
Formula details are tied to the specific inputs above and use visible unit conversions.
What changes the result the most?
Drive count, drive size, resiliency mode, mirror/parity layout, and vendor pool overhead drive usable Storage Spaces capacity.
How should I use this result?
Use it as a planning estimate and compare important decisions with product documentation, labels, quotes, local code, or qualified guidance.
Why does this page show warnings?
Warnings call out assumptions that can materially change the result or create safety, cost, or reliability problems.
Can I share this scenario?
Yes. The share button copies a URL with the current inputs, while the main page remains the base calculator URL.
Method details
Updated: June 24, 2026. Calculation method: WINDOWS_STORAGE_SPACES-1.0. Availability: planning aid while the page is improved, sourced, or differentiated.