The Subnet Calculator turns an IPv4 address and prefix into the network address, subnet mask, wildcard mask, broadcast address, usable range, and address counts. Use it when you need to prove whether two IPv4 addresses are on the same subnet rather than comparing octets by eye.
Input examples
Enter CIDR such as 192.168.10.70/26. A /26 divides a /24 into blocks of 64 addresses, so that example belongs to network 192.168.10.64/26 with ordinary host range .65–.126 and broadcast .127.
How to use the output?
The network address identifies the subnet itself; it is not normally assigned to a host. The broadcast address is the directed broadcast for traditional IPv4 subnets. The usable range shows ordinary host addresses. The wildcard mask is useful in systems that express match rules as the inverse of the subnet mask.
/31 and /32 are special cases
A /31 is used for point-to-point links under modern IPv4 practice and does not follow the classic network/broadcast host subtraction in the same way as a normal LAN. A /32 represents one host route. Do not design a DHCP client LAN from those values as though they were ordinary multi-host subnets.
Practical troubleshooting
If a client is 192.168.1.50/24 and the gateway is 192.168.2.1, they are not on the same /24 and the client cannot reach that gateway directly without another route. If a VPN advertises a prefix that overlaps the home LAN, the route table—not the popularity of 192.168.1.1—determines where traffic goes.
Limitations
Subnet math does not tell you which address a router administrator chose, whether DHCP is running, or whether a firewall allows traffic. Use the result as an addressing fact and combine it with the actual routing/DHCP configuration.
Video walkthrough for Subnet Calculator (CIDR)
Visual foundation for network/host bits, masks, CIDR and subnetting. Use the calculator on this site for the exact arithmetic after understanding the concept.
Subnet Mask Explained — PowerCert Animated Videos. Watch on YouTube