Type an address with its prefix, like 192.168.1.10/24, to get the network and broadcast addresses, the usable host range, the subnet and wildcard masks and the bits behind them. Split a network into equal parts, or switch to IPv6 for prefix details. It is free and runs in your browser.
How to use the subnet calculator, step by step
- Choose IPv4 or IPv6.
- Type the Address and prefix, such as 192.168.1.10/24. You can also type an address and a mask, like 10.0.0.0 255.255.0.0.
- Read the Details: network, broadcast, first and last host, number of hosts, and the masks. Open the Binary view to see the bits.
- To plan a network, enter the Hosts needed to find the smallest subnet that fits, or enter a Number of subnets to split the network into equal parts.
- Press Copy all details to keep the result.
Reading the results
The prefix length says how many bits at the start of the address name the network; the rest number the hosts. A /24 leaves 8 host bits, so 256 addresses. The first one is the network address and the last is the broadcast address, which leaves 254 for devices. A /31 is used for point-to-point links and has 2 usable addresses, and a /32 is a single host.
Masks and wildcards
The subnet mask is the prefix written as an address, such as 255.255.255.0 for /24. The wildcard mask is its inverse, 0.0.0.255, which is what Cisco access lists and OSPF use. You can type either a prefix or a mask, like 10.0.0.0 255.255.0.0.
Private and special ranges
10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 are private and used inside homes and offices. 100.64.0.0/10 is shared space for carrier-grade NAT, 127.0.0.0/8 is loopback and 169.254.0.0/16 shows up when a device couldn't get an address. For IPv6, fd00::/8 is the private range, fe80::/10 is link-local, 2001:db8::/32 is reserved for examples, and a /64 is the normal size for one network.
Planning a network
- Count the devices you need now and leave room to grow.
- Pick the smallest prefix that holds them with room to spare.
- Give each group, such as staff, guests and cameras, its own subnet.
- Write down your plan, including the first and last host in each range.
Who uses it
Students studying for networking exams, IT staff setting up an office or a lab, home users tidying a router setup, and developers working with cloud networks. To look up a domain, see the DNS lookup, and for file permissions, the chmod calculator.
Questions
How many usable hosts does a /24 have?
254. Two of the 256 addresses are the network and broadcast addresses.
What is a wildcard mask?
The inverse of the subnet mask, used in some router access lists.
Is my data sent anywhere?
No. The sums run in your browser.