Calculator
Use IP Address + Prefix for direct subnet analysis, or Required Hosts to let the tool recommend the smallest fitting prefix.
Example Data Table
| Prefix | Subnet Mask | Total Addresses | Usable Hosts | Typical Use |
|---|---|---|---|---|
| /24 | 255.255.255.0 | 256 | 254 | Medium office LAN |
| /26 | 255.255.255.192 | 64 | 62 | Department VLAN |
| /27 | 255.255.255.224 | 32 | 30 | Small branch segment |
| /29 | 255.255.255.248 | 8 | 6 | Infrastructure devices |
| /31 | 255.255.255.254 | 2 | 2 | Point-to-point link |
Formula Used
The calculator uses standard IPv4 subnetting rules. It derives the dotted decimal mask from the prefix, computes network and broadcast boundaries with bitwise operations, and applies special handling for /31 and /32.
How to Use This Calculator
- Select IP Address + Prefix to inspect an existing subnet.
- Select Required Hosts to find the smallest subnet that fits your host demand.
- Enter a valid IPv4 address. The tool uses it as the reference or base network address.
- Fill in the prefix or required host count.
- Optionally add planned hosts or a growth reserve.
- Press Calculate Network Size to view the subnet summary, graph, and export buttons.
Frequently Asked Questions
1) What does network size mean in IPv4?
Network size describes how many total addresses and usable host addresses exist inside a subnet. It depends on the prefix length, such as /24 or /27.
2) How is a /24 different from a /26?
A /24 provides 256 total addresses and 254 usable hosts. A /26 provides 64 total addresses and 62 usable hosts, so it is much smaller.
3) Why are two addresses usually unavailable?
In most subnets, one address is reserved for the network identifier and one for the broadcast address. That leaves total addresses minus two as usable hosts.
4) Why does /31 show two usable addresses?
A /31 is commonly used on point-to-point links. Modern networking practice allows both addresses to be used because broadcast behavior is not needed there.
5) What is the wildcard mask?
The wildcard mask is the inverse of the subnet mask. Network devices and access lists often use it to match address ranges more flexibly.
6) Can this tool help with capacity planning?
Yes. Use Required Hosts mode with a growth reserve to size a subnet that supports current demand while leaving room for future devices.
7) Why does the base IP sometimes change to another network address?
The tool aligns your entered IP to the real network boundary for the chosen prefix. That calculated boundary becomes the network address.
8) What should I export to keep subnet records?
Use CSV for spreadsheets and inventory logs. Use PDF when you want a clean shareable summary for design reviews, audits, or handoff documents.