IPv4 Subnet Calculator
Enter any IPv4 address and CIDR prefix — or type the dotted-decimal mask and let the CIDR update automatically. Get the full subnet breakdown instantly: network and broadcast addresses, usable host range, wildcard mask, IP class, address type and a colour-coded binary view that shows exactly which bits are network vs host. Correct edge-case handling for /31 (RFC 3021 point-to-point) and /32 (single host).
CIDR and subnet mask stay in sync — change either one.
Binary representation
10 Network bits (solid underline) · 10 Host bits (dotted underline)
Is an IP in this subnet?
Enter any IPv4 address to check if it falls within the current network.
Use — Guide
How to use this tool
- Enter any IPv4 address in the "IPv4 Address" field — for example, 192.168.1.10.
- Choose a CIDR prefix from the dropdown (for example, /24), or type a dotted-decimal subnet mask in the "Subnet Mask" field — both stay in sync automatically.
- Read the summary band for the network and IP class, then check the result grid for the network address, broadcast address, usable host range, host count, wildcard mask and CIDR notation.
- Scroll down to the binary representation to see exactly which bits are network bits (solid underline, green) and which are host bits (dotted underline, amber).
- Type any IPv4 address in the "Is an IP in this subnet?" section to instantly check whether it falls within the current network.
- Click any copy icon to copy a value to the clipboard.
FAQ — Questions
Frequently asked questions
01What is a subnet mask and how does it relate to CIDR?
A subnet mask (e.g. 255.255.255.0) and a CIDR prefix (e.g. /24) express the same thing differently — how many bits of an IP address identify the network versus the host. CIDR notation is more compact and is standard in modern routing. This calculator keeps both in sync so you can enter either one.
02How many usable hosts does a /24 subnet have?
A /24 gives you 256 total addresses (2^8), but the network address (.0) and broadcast address (.255) are reserved, leaving 254 usable hosts. The same formula applies to any prefix: 2^(32 minus prefix) minus 2 usable hosts, except /31 (RFC 3021 point-to-point, 2 hosts with no reserved addresses) and /32 (single host).
03What is the wildcard mask used for?
The wildcard mask is the bitwise inverse of the subnet mask. It's used in Cisco ACLs and OSPF area statements to specify which bits to match. For a /24 (mask 255.255.255.0), the wildcard is 0.0.0.255 — meaning 'match any value in the last octet'.
04Is this data sent to a server?
No. All subnet calculations run entirely in your browser using JavaScript. No IP addresses or network data are transmitted to Peritus Digital or any third party.
More — Keep exploring
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