IPv4 Subnet Calculator
Network, broadcast, usable host range, wildcard mask and binary view for any IPv4 address and CIDR prefix.
Planning a VLAN, sizing a DHCP scope or checking whether two hosts share a subnet starts with the same numbers: network address, broadcast, usable range and mask. Type any IPv4 address with a prefix – or pick a dotted mask – and every value updates as you type, including the binary view that shows exactly where the network bits end.
How to use it
- Enter an address and prefix, e.g.
10.20.0.130/25. Without a prefix the calculator uses the mask you choose (or the classful default). - Read the network, broadcast and usable host range. Copy any value with one click.
- To carve the network up, choose Split into subnets of – for example /27 – to list every subnet with its usable range.
Practical sizing guide
/30– 2 hosts: legacy point-to-point links (use/31on modern routers)./28– 14 hosts: a small DMZ or management network./24– 254 hosts: the classic office LAN./22– 1,022 hosts: campus or Wi-Fi networks that need room to grow.
From the field
Leave space between subnets when you allocate them. Giving each site a /23 even if it only needs a /24 today avoids renumbering when it grows – renumbering a live network is far more expensive than unused addresses.
Frequently asked questions
What is a CIDR prefix?
The number after the slash (for example /24) says how many leading bits of the address belong to the network. /24 equals the mask 255.255.255.0 and leaves 8 bits – 254 usable addresses – for hosts.
Why are two addresses not usable?
In a normal subnet the first address identifies the network and the last is the broadcast address. /31 links (RFC 3021) and /32 host routes are the exceptions, and the calculator handles both.
What is a wildcard mask used for?
A wildcard mask is the inverse of the subnet mask. Cisco ACLs and OSPF network statements use it to match a range of addresses.
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