Subnet Calculator
Enter any IPv4 address and CIDR prefix (/0 through /32) and get the network address, broadcast, subnet mask, wildcard mask, host range, and totals — all computed locally in your browser.
One IP and prefix, full breakdown
Every CIDR collapses to a numeric range. The calculator extracts the network, the broadcast, the mask shape, and where your usable hosts live.
10.0.0.42/22
Network: 10.0.0.0 Broadcast: 10.0.3.255 Mask: 255.255.252.0 Wildcard: 0.0.3.255 First: 10.0.0.1 Last: 10.0.3.254 Hosts: 1022
What you'll use this for
From classroom networking labs to designing real production VPCs, the subnet calculator answers the boring-but-critical questions.
VPC & cloud subnetting
Carve up 10.0.0.0/16 into AWS, GCP or Azure subnets without an off-by-one bug.
Router config
Convert between dotted mask and CIDR for IOS, JunOS, MikroTik and Linux iproute2.
Networking exams
Verify CCNA / Network+ practice problems and double-check ACL math.
Firewall rules
Translate a prefix into a wildcard mask for an ACL or compute the broadcast for a NAT rule.
How to use the subnet calculator
Enter the IPv4 address
Type any dotted-quad address such as 172.16.32.10. The address itself can be a network, host, or broadcast — the prefix decides.
Pick a CIDR prefix
Any value from /0 (the whole internet) to /32 (a single host). Common LAN sizes are /24, /27, and /30.
Read the breakdown
Network and broadcast addresses, masks, host range, and totals appear instantly. /31 and /32 follow RFC 3021.
Copy the result
Click to copy the entire breakdown as plain text — paste it into a doc, a ticket, or a router config.
Frequently asked questions
A subnet mask has 1s for the network portion and 0s for the host portion. A wildcard mask is the bitwise inverse — 0s for the network and 1s for the host — and is what Cisco ACLs accept.
RFC 3021 allows /31 networks for point-to-point links, where both addresses are usable because there's no broadcast on a two-node segment. /32 is treated as a single host route.
The broadcast is the network address OR'd with the bitwise inverse of the mask — every host bit set to 1. For 10.0.0.0/22, that's 10.0.3.255.
Each step in prefix doubles the host count. /24 = 256 addresses, /23 = 512, /22 = 1024, and so on. Subtract 2 (network + broadcast) for usable hosts on prefixes /30 and shorter.
This tool focuses on IPv4. For IPv6 prefix math, use our IPv4 to IPv6 converter or follow up with the CIDR Calculator.
About IPv4 subnetting
Classless Inter-Domain Routing (RFC 4632) replaced the old class-A/B/C system in 1993 with a single number — the prefix length — that says how many leading bits of the address identify the network. Everything below subnetting comes down to that one slash.
Key terms
- Network address — first address in the block, all host bits zero.
- Broadcast address — last address, all host bits set; sends to every host on the segment.
- Subnet mask — the dotted-quad form of the prefix.
- Wildcard mask — bitwise inverse of the subnet mask; used by Cisco ACLs.
Common prefix sizes
/30— 4 addresses, 2 usable. Point-to-point links./29— 8 addresses, 6 usable. Small subnet for a handful of devices./24— 256 addresses, 254 usable. Classic "Class C" LAN./16— 65,536 addresses. Often the top-level VPC range.