{
    "name": "RAID Capacity Calculator",
    "url": "https://calculators.geekmidst.com/calculators/raid-capacity-calculator",
    "markdown": "https://calculators.geekmidst.com/calculators/raid-capacity-calculator.md",
    "category": "IT, networking & security",
    "description": "Work out usable storage for RAID 0, 1, 5, 6 and 10 from the number and size of drives, in decimal TB and binary TiB, with fault tolerance and efficiency.",
    "summary": "RAID gives up some capacity for redundancy: one drive’s worth for RAID 5, two for RAID 6, half for RAID 10. Drive makers quote decimal TB, while many operating systems show binary TiB.",
    "also_called": [
        "RAID storage calculator",
        "NAS capacity calculator"
    ],
    "applies_to": "Worldwide",
    "last_updated": "2026-10-29",
    "computation": "Results are computed in the visitor’s browser on the HTML page. This API describes the calculator; it does not compute results.",
    "inputs": [
        {
            "name": "level",
            "label": "RAID level",
            "type": "select",
            "default": "6",
            "options": {
                "0": "RAID 0 (striping)",
                "1": "RAID 1 (mirror)",
                "5": "RAID 5 (single parity)",
                "6": "RAID 6 (double parity)",
                "10": "RAID 10 (striped mirrors)"
            }
        },
        {
            "name": "drives",
            "label": "Number of drives",
            "type": "number",
            "default": "6"
        },
        {
            "name": "spares",
            "label": "Hot spares",
            "type": "number",
            "default": "0",
            "optional": true
        },
        {
            "name": "drive_size",
            "label": "Drive size",
            "type": "number",
            "default": "4"
        },
        {
            "name": "size_unit",
            "label": "Size unit",
            "type": "segmented",
            "default": "TB",
            "options": {
                "TB": "TB",
                "GB": "GB"
            }
        }
    ],
    "outputs": [
        {
            "key": "usable_tb",
            "label": "Usable capacity",
            "format": "number"
        },
        {
            "key": "usable_tib",
            "label": "Usable capacity (binary)",
            "format": "number"
        },
        {
            "key": "raw_tb",
            "label": "Raw capacity",
            "format": "number"
        },
        {
            "key": "overhead_tb",
            "label": "Redundancy and spares",
            "format": "number"
        },
        {
            "key": "efficiency",
            "label": "Storage efficiency",
            "format": "percent"
        },
        {
            "key": "fault_tolerance",
            "label": "Drive failures survived",
            "format": "text"
        }
    ],
    "formula": {
        "text": "Usable = Data drives × Drive size, where data drives = n (RAID 0), 1 (RAID 1), n − 1 (RAID 5), n − 2 (RAID 6), n ÷ 2 (RAID 10), n = drives − hot spares;  TiB = bytes ÷ 2⁴⁰",
        "variables": {
            "n": "active drives in the array",
            "Drive size": "decimal: 1 TB = 10¹² bytes"
        }
    },
    "worked_example": {
        "inputs": {
            "level": "6",
            "drives": "6",
            "spares": "0",
            "drive_size": "4",
            "size_unit": "TB"
        },
        "steps": [
            "RAID 6 uses two drives’ worth of parity: 6 − 2 = 4 data drives.",
            "4 × 4 TB = 16 TB = 16 × 10¹² bytes.",
            "16 × 10¹² ÷ 2⁴⁰ = 14.552 TiB; 16 ÷ 24 TB raw = 66.67%."
        ],
        "result": "Six 4 TB drives in RAID 6 give 16 TB (14.55 TiB) usable and survive any two drive failures."
    },
    "interpretation": "Leave free space for file-system metadata and snapshots, and remember RAID is not a backup: deletion, corruption and ransomware are copied to every drive.",
    "assumptions": [
        "All drives are the same size; with mixed sizes most RAID levels use only the smallest size on every drive."
    ],
    "limitations": [
        "File-system overhead, ZFS/Btrfs specifics and vendor RAID variants (RAID-Z, SHR) are not modelled."
    ],
    "rules": null,
    "faqs": [
        {
            "question": "Why does my 4 TB drive show 3.64 TB?",
            "answer": "The drive has 4 × 10¹² bytes. Windows divides by 2⁴⁰ and shows 3.64, but labels it “TB” rather than TiB."
        },
        {
            "question": "RAID 6 or RAID 10?",
            "answer": "RAID 6 survives any two failures and gives more space with many drives; RAID 10 gives better write performance and faster rebuilds but can be lost if both drives in one mirror fail."
        }
    ],
    "sources": [],
    "related": [
        {
            "name": "RAID Rebuild Time Calculator",
            "url": "https://calculators.geekmidst.com/calculators/raid-rebuild-time-calculator"
        },
        {
            "name": "Database Backup Window Calculator",
            "url": "https://calculators.geekmidst.com/calculators/database-backup-window-calculator"
        },
        {
            "name": "Cloud Storage Cost Calculator",
            "url": "https://calculators.geekmidst.com/calculators/cloud-storage-monthly-cost-calculator"
        }
    ],
    "disclaimer": null,
    "publisher": "GM¹X CalcVerse"
}