IP/CIDR Calculator

Enter any IPv4 CIDR block to get the network address, broadcast address, usable host range, netmask and host count — computed locally.

Network

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Netmask

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First host

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Last host

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Broadcast

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Usable hosts

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CIDR

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Total addresses

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Usable hosts = total − 2, except /31 (point-to-point) and /32 (single host) where all addresses are usable.

Walkthrough

How to use it

Type a CIDR block like 192.168.1.0/24 — a bare IP defaults to /32.
Press Calculate or Enter.
Read the network, netmask, host range, broadcast and counts.
Wondering if two subnets overlap or if an IP is inside the range? Check the FAQ below.

Use cases

When you'd use this

VPC and firewall planning. Verify a proposed subnet fits inside its parent block and has enough host space.

IP allowlists. Expand a CIDR entry in a security group to confirm which IPs it covers.

DHCP ranges. Derive the first/last usable addresses when configuring a DHCP pool.

FAQ

Common questions

How do I check whether one subnet contains another?

Calculate the parent block, then check that the child's network address is between the parent's first and last host addresses. Equivalently: the child's network must be within the parent's total range.

What does /24, /25 etc. mean?

The number after the slash is the number of fixed bits in the network mask. /24 = 255.255.255.0 and 256 addresses; /25 = 128; each +1 halves the block.

Why does /31 give 2 usable hosts instead of 0?

RFC 3021 defines point-to-point links, so both addresses are usable. This calculator applies that rule for /31 and /32.