Subnet Calculator
Calculate the full IPv4 subnet details for any IP address and CIDR prefix. Enter an address such as 192.168.1.0/24 and this tool instantly shows the network address, broadcast address, subnet mask, usable host range and total host count — all computed in your browser.
What Is a Subnet Calculator?
A subnet calculator is a tool that takes an IP address plus a CIDR (Classless Inter-Domain Routing) prefix and works out the boundaries of the network that address belongs to. When you write 192.168.1.0/24, the /24 tells you how many of the 32 bits in an IPv4 address are fixed as the network portion — the remaining bits are available for host addresses inside that subnet.
From just those two numbers the calculator derives everything a network engineer needs: the network address (the first address, identifying the subnet itself), the broadcast address (the last address, used to reach every host at once), the subnet mask (the dotted-decimal form of the prefix, such as 255.255.255.0), the usable host range, and how many hosts the subnet can actually hold.
How to Use This Tool
- Type an IP address followed by a CIDR prefix — for example
192.168.1.0/24,10.0.0.0/8or172.16.5.128/25. - Press Calculate (or hit Enter).
- Read the results in the table: network, broadcast, mask, host range and host count.
- Use it to plan VLANs, split an office network, or verify that an address belongs to the range you expect.
Everything runs entirely on your device — your IP address is never sent anywhere, so you can freely calculate private or internal ranges without any privacy concern.
Subnet Calculator — Frequently Asked Questions
What is CIDR notation?
CIDR (Classless Inter-Domain Routing) notation writes an IP address followed by a slash and a number, such as 192.168.1.0/24. The number after the slash is the prefix length: it tells you how many of the address's bits are fixed as the network portion. A larger number means a smaller network. For example, /24 leaves 8 bits for hosts (256 addresses), while /16 leaves 16 bits for hosts (65,536 addresses).
What is a subnet mask?
A subnet mask is a 32-bit number, written in dotted-decimal like 255.255.255.0, that marks which bits of an IP address belong to the network and which belong to the host. In binary, the mask has a run of 1s (the network part) followed by 0s (the host part). The CIDR prefix and the subnet mask are two ways of saying the same thing: /24 is equivalent to 255.255.255.0.
How many hosts can a subnet hold?
The number of addresses in a subnet is 2 raised to the number of host bits. For a /24 there are 8 host bits, so 28 = 256 addresses. However, the network address and the broadcast address cannot be assigned to devices, so the number of usable hosts is 28 − 2 = 254. This calculator reports both the total and the usable host count.
What are the network and broadcast addresses?
The network address is the first address in a subnet and is used to identify the subnet itself; it cannot be assigned to a device. The broadcast address is the last address in the subnet and is used to send a message to every host on that network at once; it also cannot be assigned to a device. The usable host range runs between these two endpoints.
Is this subnet calculator free and private?
Yes. This tool is completely free and runs entirely in your browser. The calculation is done locally in JavaScript, so the IP address and CIDR prefix you enter are never transmitted to any server, logged, or stored.