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IPv4 Subnet Calculator

Enter any IPv4 address and CIDR prefix to instantly calculate network details including subnet mask, host range, broadcast address, and more. A free tool by IPv4Center.

What Is Subnetting?

Subnetting is the practice of dividing a larger IP network into smaller, more manageable sub-networks (subnets). It improves network performance, enhances security by isolating segments, and makes efficient use of limited IPv4 address space. Each subnet is defined by a network address and a subnet mask that determines how many host addresses are available within it. Learn more in our subnetting guide.

How Subnet Calculators Work

A subnet calculator takes an IPv4 address and a CIDR prefix length (e.g., /24) and performs bitwise operations to determine the network address, broadcast address, valid host range, and subnet mask. The CIDR prefix indicates how many leading bits of the 32-bit IP address represent the network portion — the remaining bits are available for host addresses within that subnet.

Common Subnet Reference

CIDRSubnet MaskUsable Hosts
/32255.255.255.2551
/31255.255.255.2542 (point-to-point)
/30255.255.255.2522
/29255.255.255.2486
/28255.255.255.24014
/27255.255.255.22430
/26255.255.255.19262
/25255.255.255.128126
/24255.255.255.0254
/23255.255.254.0510
/22255.255.252.01,022
/21255.255.248.02,046
/20255.255.240.04,094
/19255.255.224.08,190
/18255.255.192.016,382
/17255.255.128.032,766
/16255.255.0.065,534
/8255.0.0.016,777,214

Frequently Asked Questions

What is a subnet mask?▼
A subnet mask is a 32-bit number that separates an IP address into its network and host portions. It uses consecutive 1-bits for the network part and 0-bits for the host part. For example, 255.255.255.0 (/24) means the first 24 bits identify the network and the remaining 8 bits identify individual hosts.
What is CIDR notation?▼
CIDR (Classless Inter-Domain Routing) notation is a compact way to specify an IP address and its associated subnet mask. It uses a forward slash followed by the number of network bits — for example, 192.168.1.0/24 means the first 24 bits are the network portion.
How many usable hosts does a /24 subnet have?▼
A /24 subnet has 256 total addresses (2^8). Two addresses are reserved: one for the network address and one for the broadcast address, leaving 254 usable host addresses.
What is the difference between a network address and a broadcast address?▼
The network address is the first address in a subnet and identifies the subnet itself — it cannot be assigned to a host. The broadcast address is the last address and is used to send data to all hosts within the subnet simultaneously.
What is a wildcard mask?▼
A wildcard mask is the inverse of a subnet mask. Where the subnet mask has 1-bits, the wildcard mask has 0-bits, and vice versa. Wildcard masks are commonly used in access control lists (ACLs) and routing protocols like OSPF to match ranges of IP addresses.
How do /31 and /32 subnets work?▼
A /31 subnet has 2 addresses and is used for point-to-point links between two routers (RFC 3021) — both addresses are usable. A /32 subnet represents a single host address and is used for loopback interfaces, host routes, and specific routing configurations.
What are private IP address ranges?▼
RFC 1918 defines three private IPv4 ranges: 10.0.0.0/8 (Class A), 172.16.0.0/12 (Class B), and 192.168.0.0/16 (Class C). These addresses are not routable on the public internet and are used within local area networks.
What are IP address classes?▼
IPv4 addresses were originally divided into five classes: Class A (1.0.0.0 – 126.255.255.255), Class B (128.0.0.0 – 191.255.255.255), Class C (192.0.0.0 – 223.255.255.255), Class D (224.0.0.0 – 239.255.255.255, multicast), and Class E (240.0.0.0 – 255.255.255.255, reserved). While classful addressing has been replaced by CIDR, the terminology is still widely used. See our IP address classes guide for details.

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