Allocate addresses with confidence across any network. Choose CIDR, hosts, or subnets, then calculate quickly. Download CSV and PDF reports for audits and planning.
| Base network | Segments | Requested hosts | Notes |
|---|---|---|---|
| 192.168.10.0/24 | HQ, Warehouse, Sales, Guest | 120, 60, 28, 12 | Sorted and allocated largest-first for efficiency. |
| 10.20.0.0/22 | Apps, DB, CI, VPN | 400, 180, 60, 30 | Leaves contiguous space for growth and new segments. |
Run these samples in VLSM mode to see assigned subnets, usable ranges, and exported reports.
This calculator reports total addresses, usable hosts, and reserved addresses for each prefix. For example, a /24 contains 256 addresses, 254 usable hosts, and 2 reserved. A /27 contains 32 addresses, 30 usable, and 2 reserved. These numbers help quantify utilization. Tracking these ratios highlights renumbering opportunities.
In fixed-length mode, the new prefix is derived from either the subnet count or the host target. If you request 8 equal subnets from a /24, the tool adds 3 bits, producing /27 blocks. Each /27 yields 30 usable hosts. That means the /24 becomes 8 segments with 240 usable hosts total, plus 16 reserved addresses. If you instead size for 50 hosts, the next power-of-two block is 64, so the prefix becomes /26 and delivers 62 usable.
VLSM mode sorts requirements largest-first, then assigns the smallest power-of-two block that fits each request plus overhead. A 120-host segment typically maps to a /25 block (128 addresses, 126 usable). A 60-host segment maps to /26 (64 addresses, 62 usable). This approach reduces waste compared with forcing every segment into the same size.
To keep allocations clean, each VLSM block is aligned on its natural boundary. A /26 must start at a multiple of 64 addresses within the base range. Alignment prevents overlaps and makes route summarization easier. If alignment pushes an allocation beyond the base broadcast address, the tool flags insufficient space instead of guessing.
Exported CSV and PDF reports capture network, mask, broadcast, and usable ranges for each planned subnet. These fields support firewall objects, DHCP scopes, and IPAM imports. Including both first and last usable addresses reduces on-call errors when creating static reservations or troubleshooting overlapping pools.
The input layer validates IPv4 formatting and ensures the subnet mask is contiguous. The calculator also caps displayed FLSM rows to avoid browser overload while still exporting full summaries. Special handling for /31 and /32 provides accurate host counts for point-to-point links and loopbacks in modern routing designs. Confirm the base address is a network boundary.
Use the network address of your block, such as 192.168.10.0 for a /24. Using a host address can shift results and make summaries harder to interpret.
Yes. Provide a contiguous IPv4 mask like 255.255.255.0. If both fields are filled, the CIDR prefix takes priority for calculation.
Each segment gets the next power-of-two address block that can hold requested hosts plus network and broadcast overhead. The tool then derives the prefix from that block size.
A /31 provides two addresses commonly used on point-to-point links, so both can be treated as usable. A /32 represents a single address, often used for loopbacks.
The tool stops allocating once the next segment would extend beyond the base broadcast address. It adds a warning so you can enlarge the base prefix or reduce requirements.
No. CSV and PDF exports are generated from the last computed tables stored in your session. Recalculate after edits to ensure the exports reflect your latest inputs.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.