Subnet Calculator
Calculate IPv4 subnet details from an IP and CIDR prefix or subnet mask — network and broadcast address, usable host range, host count, wildcard mask, and more, entirely in your browser.
Enter an IPv4 address with a CIDR prefix (192.168.1.130/24) or a subnet mask (192.168.1.130 255.255.255.0). A bare address assumes /24.
ToolsSoup's Subnet Calculator is a free online IPv4 subnet calculator that runs entirely in your browser. Enter an IP address with a CIDR prefix (like 192.168.1.130/24) or a dotted subnet mask, and instantly get the network address, broadcast address, subnet mask, wildcard mask, the usable host range, the number of total and usable hosts, the IP class, and whether the address is private or public. Every value is computed locally on your device — nothing is ever sent to a server.
What is a subnet calculator?
A subnet calculator takes an IPv4 address and a subnet size and works out the boundaries of the network it belongs to. From the prefix length (or the equivalent subnet mask) it derives the network address (the first address in the block, used to identify the network), the broadcast address (the last address, used to reach every host at once), the subnet mask and its wildcard mask, the range of addresses you can actually assign to devices, and how many hosts that range holds. It is the everyday tool network engineers use to plan IP ranges, split a network into smaller subnets, and double-check VLSM and CIDR designs.
How to use the subnet calculator
Getting a full subnet breakdown takes only a moment:
- Type an IPv4 address followed by a CIDR prefix, for example 10.0.0.5/16. You can also enter a dotted subnet mask instead, like 10.0.0.5 255.255.0.0.
- Click Calculate, or just press Enter.
- Read the results: network and broadcast addresses, subnet and wildcard masks, the first and last usable host, the usable host count, and the IP class.
Network, broadcast, and usable hosts explained
In a normal subnet, the first address is the network address and the last is the broadcast address; neither can be assigned to a device, so the usable hosts are everything in between. That is why a /24 has 256 total addresses but only 254 usable hosts. Point-to-point /31 links (RFC 3021) use both addresses as hosts, and a /32 describes a single host with no broadcast address — this calculator handles those special cases for you.
Why use this subnet calculator?
- Accepts either CIDR prefix notation (/24) or a dotted-decimal subnet mask (255.255.255.0).
- Shows the network address, broadcast address, and the exact first-to-last usable host range.
- Reports total addresses and usable host count, including the /31 and /32 special cases.
- Derives the wildcard mask and binary mask for ACL and router configuration work.
- Runs 100% in your browser with no network requests, so it works offline and keeps your data private.
Frequently asked questions
What is the difference between a CIDR prefix and a subnet mask?
They describe the same thing two ways. A CIDR prefix like /24 counts the number of leading network bits, while the subnet mask 255.255.255.0 writes those same bits out in dotted-decimal form. This calculator accepts either, so you can enter 192.168.1.0/24 or 192.168.1.0 255.255.255.0 and get identical results.
Why does a /24 have 254 usable hosts instead of 256?
A /24 block contains 256 addresses, but the first one is reserved as the network address and the last one is reserved as the broadcast address. Those two cannot be assigned to devices, leaving 254 usable host addresses for a standard subnet.
How do I calculate the broadcast address?
The broadcast address is the last address in the subnet: take the network address and set every host bit to 1 (equivalently, OR the IP with the wildcard mask). For 192.168.1.130/24 the network is 192.168.1.0 and the broadcast is 192.168.1.255. The calculator does this for you automatically.
What is a wildcard mask?
A wildcard mask is the bitwise inverse of the subnet mask, so for 255.255.255.0 the wildcard is 0.0.0.255. Cisco access control lists and OSPF configurations use wildcard masks instead of subnet masks to specify address ranges.
Does this tool send my IP address anywhere?
No. All subnet math runs locally in your browser using simple bitwise arithmetic, with no network requests. The tool works offline and never transmits the addresses you enter.