Tool · Networking
Subnet Calculator (IPv4)
Enter an address with a prefix or subnet mask and get the network address, broadcast, the range you can give to devices, subnet mask, wildcard mask and the bits behind them. You can also split the network into smaller subnets.
When you need it
- Static addresses: before you give a printer, NAS or server a fixed address, you need to know which addresses actually belong to your network – and which one the router hands out itself.
- Firewall and access rules: many admin interfaces expect whole networks in CIDR notation, some routers want a wildcard mask instead. The calculator shows both.
- Splitting a network: a guest Wi-Fi, cameras or a lab each get their own block of addresses that must not overlap with the others.
- Troubleshooting: two devices cannot reach each other? Quite often they sit in different networks because one of them has the wrong mask.
CIDR notation and subnet masks
An IPv4 address has 32 bits, written as four numbers from 0 to 255. The bits at the front
identify the network, the ones at the back the host (the
device) within that network. The prefix says where the line is drawn:
/24 means the first 24 bits belong to the network. Writing it like this is
called CIDR notation.
The subnet mask says the same thing another way: as many ones at the front as
the prefix length, zeros after that. /24 is 255.255.255.0. The
wildcard mask is the inverse (0.0.0.255) and turns up in some router
and firewall rules.
A prefix /n covers 232−n addresses: 256 for a /24, 65,536 for a /16 and 16,777,216 for a /8.
How the calculator works
- Network address = address AND mask: every host bit is set to 0.
- Broadcast address = network address OR wildcard: every host bit is set to 1.
- Neither of the two may be given to a device. Everything in between is usable: from network address + 1 to broadcast − 1, which makes 232−n − 2 addresses.
- Splitting into subnets with a longer prefix m gives 2m−n networks of 232−m addresses each, one directly after the other.
Worked example
Take 192.168.1.10/24 – the address the calculator shows when you open it:
| Address | 11000000.10101000.00000001.00001010 | 192.168.1.10 |
|---|---|---|
| Mask /24 | 11111111.11111111.11111111.00000000 | 255.255.255.0 |
| AND → network | 11000000.10101000.00000001.00000000 | 192.168.1.0 |
| Host bits to 1 | 11000000.10101000.00000001.11111111 | 192.168.1.255 |
The network has 28 = 256 addresses. Take away the network and broadcast addresses and
254 are left for devices: 192.168.1.1 to 192.168.1.254.
Split it into /26 networks and you get 22 = 4 subnets of 64 addresses,
62 of them usable: 192.168.1.0/26, 192.168.1.64/26,
192.168.1.128/26 and 192.168.1.192/26.
Special cases: /31 and /32
- /31 has only two addresses. Under the normal rule none would be left for devices. For point-to-point links between two routers, RFC 3021 therefore allows both addresses to be used, and there is no broadcast address. The calculator treats /31 this way.
- /32 is exactly one address – for example a single host in a firewall rule or a host route in a routing table.
Typical home networks
At home, the router hands out addresses from one of the private ranges defined
in RFC 1918: 10.0.0.0/8, 172.16.0.0/12 or 192.168.0.0/16.
They cannot be reached from the internet; on the way out the router translates them to the
public address of your connection (NAT).
A /24 home network has 254 usable addresses. If the public address your router reports lies in
100.64.0.0/10, you do not have a public IPv4 address of your own: that range is
reserved for carrier-grade NAT at your provider (RFC 6598). The calculator points out this and
other special-purpose ranges.
Limits of this tool
- IPv4 only. IPv6 prefixes may follow later.
- It only splits into subnets of equal size; it does not plan networks of different sizes by number of hosts (VLSM).
- It does not check whether a network is reachable or already in use in your environment.
- The special-purpose ranges are a selection from the IANA registry (retrieved 23 October 2026) plus multicast. Anything added there later is unknown to the tool until it is updated.
Privacy: the calculator runs entirely in your browser. What you enter is not sent to xmoo.app or anyone else.
Sources
- 32-bit IPv4 addresses: RFC 791
- CIDR, prefix notation, addresses per prefix (/24 = 256, /16 = 65,536, /8 = 16,777,216, /32 = “host route”): RFC 4632
- Network and broadcast address, loopback
127.0.0.0/8: RFC 1122, section 3.2.1.3 - /31 on point-to-point links: RFC 3021
- Private ranges: RFC 1918;
shared address space
100.64.0.0/10: RFC 6598 - Special-purpose ranges (link-local, documentation, benchmarking, reserved, limited broadcast and others): IANA IPv4 Special-Purpose Address Registry (retrieved 23 October 2026)
- Multicast 224.0.0.0 to 239.255.255.255: RFC 5771
Page last updated: 30 October 2026