Subnet Calculator
Calculate IPv4 network, broadcast, host range and masks from a CIDR
About Subnet Calculator
Takes an IPv4 address with a /prefix or a dotted netmask and shows the network and broadcast addresses, usable host range and count, wildcard mask, class, address type and binary and hex forms, all computed client-side. It can also split the block into smaller subnets, listing up to 256 of them, but it does not handle IPv6. Useful for planning VPCs, firewall rules and DHCP scopes.
Category: API.
Frequently asked questions
Which input formats are accepted?
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CIDR notation such as 192.168.1.10/24, or an address followed by a dotted netmask after a slash or a space, as in 192.168.1.10 255.255.255.0. Octets with leading zeros and non-contiguous masks are rejected, and a wildcard mask such as 0.0.0.255 triggers a hint with the matching netmask.
How are /31 and /32 networks handled?
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A /31 is treated as a point-to-point link under RFC 3021, so both addresses count as usable hosts and there is no broadcast address. A /32 is a single host, and its network, first host and last host are all the same address.
Which special address ranges does it recognize?
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Private RFC 1918 blocks, loopback (127.0.0.0/8), link-local (169.254.0.0/16), shared CGNAT space (100.64.0.0/10), multicast, the TEST-NET documentation blocks and reserved ranges such as 0.0.0.0/8, 198.18.0.0/15 and 240.0.0.0/4; anything else is shown as public. The type describes the address you enter, not the whole block.
How many subnets does the split view list?
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Pick any longer prefix and it lists the first 256 resulting subnets with their network, usable range and broadcast, while reporting the full count, such as 65,536 when a /8 is split into /24 networks. The copy button copies the listed rows as tab-separated text.