NetKit Subnet
Subnetting reference
IPv4 subnet cheat sheet
Find the mask and address count for a CIDR prefix, then use the worked examples to calculate a network range or split a subnet.
For a standard IPv4 subnet, a /24 contains 256 addresses and normally has 254 usable host addresses. A /26 contains 64 addresses and normally has 62 usable hosts. Cloud networks have their own reservation rules, so these conventional host counts are not cloud capacity estimates.
CIDR prefixes, masks and host counts
The prefix is the number of network bits in a 32-bit IPv4 address. The remaining bits determine the block size: 2^(32 − prefix) addresses. For ordinary broadcast subnets through /30, subtract two for the network and broadcast addresses.
| CIDR | Subnet mask | Total addresses | Usable hosts |
|---|---|---|---|
| /16 | 255.255.0.0 | 65,536 | 65,534 |
| /17 | 255.255.128.0 | 32,768 | 32,766 |
| /18 | 255.255.192.0 | 16,384 | 16,382 |
| /19 | 255.255.224.0 | 8,192 | 8,190 |
| /20 | 255.255.240.0 | 4,096 | 4,094 |
| /21 | 255.255.248.0 | 2,048 | 2,046 |
| /22 | 255.255.252.0 | 1,024 | 1,022 |
| /23 | 255.255.254.0 | 512 | 510 |
| /24 | 255.255.255.0 | 256 | 254 |
| /25 | 255.255.255.128 | 128 | 126 |
| /26 | 255.255.255.192 | 64 | 62 |
| /27 | 255.255.255.224 | 32 | 30 |
| /28 | 255.255.255.240 | 16 | 14 |
| /29 | 255.255.255.248 | 8 | 6 |
| /30 | 255.255.255.252 | 4 | 2 |
| /31 | 255.255.255.254 | 2 | 2 (point-to-point) |
| /32 | 255.255.255.255 | 1 | 1 (single address) |
A smaller prefix means a larger block. A /25 is half the size of a /24, and a /26 is one quarter of a /24. The table assumes conventional IPv4 addressing; it does not apply to IPv6.
Worked example: 192.168.10.34/26
- Find the block size. There are six host bits: 32 − 26 = 6. That gives 64 addresses.
- Find the boundaries. Within 192.168.10.0/24, /26 blocks start at .0, .64, .128 and .192. Address .34 falls in the first block.
- Read the range. The network is 192.168.10.0/26 and the broadcast address is 192.168.10.63.
- Find the host range. Conventional usable addresses run from 192.168.10.1 through 192.168.10.62: 62 hosts.
The mask is 255.255.255.192. Its inverse, the wildcard mask, is 0.0.0.63. An input such as 192.168.10.34/26 describes an address inside the block; 192.168.10.0/26 names the network itself.
Split a /24 into four equal subnets
Splitting into four uses two additional network bits, because 2² = 4. Start with 192.168.10.0/24 and increase the prefix to /26:
- 192.168.10.0/26 — hosts .1 through .62; broadcast .63.
- 192.168.10.64/26 — hosts .65 through .126; broadcast .127.
- 192.168.10.128/26 — hosts .129 through .190; broadcast .191.
- 192.168.10.192/26 — hosts .193 through .254; broadcast .255.
The blocks cover the original /24 without overlap. Together they have 248 conventional host addresses, compared with 254 before splitting, because each new subnet reserves its own network and broadcast addresses.
When subtracting two is wrong
On a /31 point-to-point link, both addresses can identify endpoints under RFC 3021. This is a special use, not a two-host replacement for an ordinary LAN. A /32 identifies a single IPv4 address and is often used for a host route.
Cloud providers reserve addresses separately. Use provider-specific rules when planning AWS, Azure or Google Cloud networks rather than subtracting two from this table. See NetKit Subnet’s cloud-aware calculations.
Check a subnet on your iPhone
NetKit Subnet accepts CIDR notation, subnet masks and wildcard masks, and shows the network, broadcast and usable range as you type. It also supports splitting networks and IPv6. Explore the NetKit Subnet app or read the input-format help.
Reference: RFC 4632: CIDR and prefix notation. Published October 3, 2026 by Fidget Digit Studios L.L.C.