Subnet Calculator (IPv4 CIDR)
Type an address like 192.168.1.10/24 and see the network, usable range, netmask, wildcard and more. Then split it into smaller subnets for VLANs, firewall rules or cloud security groups.
🔒 Runs entirely in your browser. Nothing you type is sent anywhere.
How to use it
- Type an IPv4 address with its prefix, such as
192.168.1.10/24, or with a netmask, such as10.0.0.5 255.255.255.0. - Read off the network address, the first and last usable addresses, the broadcast address and the netmask.
- To plan VLANs or smaller networks, pick a size under Split this network and copy the subnets you need.
What the results mean
- Network: the first address in the range. It identifies the subnet and isn’t given to a device.
- Broadcast: the last address. Traffic sent here reaches every device on the subnet, so it isn’t given to a device either.
- Usable hosts: the addresses you can assign to servers, PCs, printers and so on.
- Netmask and prefix are two ways of writing the same thing:
/24is255.255.255.0. - Wildcard: the netmask inverted. Cisco ACLs and some firewall rules use it.
Handy sizes for a home lab or small office
| Prefix | Usable hosts | Typical use |
|---|---|---|
| /30 | 2 | A link between two routers |
| /29 | 6 | A handful of servers or public IPs |
| /28 | 14 | A small DMZ or management VLAN |
| /27 | 30 | IoT devices or cameras |
| /26 | 62 | A guest Wi-Fi network |
| /24 | 254 | A typical home or office LAN |
| /23 | 510 | A larger office LAN |
FAQ
Why does a /31 show two usable hosts? On point-to-point links between two routers, RFC 3021 lets you use both addresses because there’s no need for a network or broadcast address. Most modern routers, including pfSense, support it.
Which ranges are private?
10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 (RFC 1918). The calculator also flags CGNAT (100.64.0.0/10), which some ISPs and Tailscale use.
Does it do IPv6? Not yet; this one is IPv4 only.
Is anything sent to a server? No. The maths runs in your browser.