netmask calculator

IPv4 Netmask Calculator

Enter an IPv4 address and either a CIDR prefix or subnet mask to calculate network details instantly.

IPv4 Address

CIDR Prefix Length (0-32)

Subnet Mask (optional if CIDR is provided)

Why a Netmask Calculator Matters

If you work with networks, cloud infrastructure, firewalls, VPNs, or even home lab routers, you run into subnetting constantly. A netmask calculator removes mental math and helps you quickly identify your network address, broadcast address, usable host range, and total number of addresses.

This is especially useful when you are planning IP allocations, troubleshooting connectivity, writing ACL rules, or validating route entries. Small mistakes in subnetting can cause hard-to-find outages. A quick calculator check can save a lot of time.

What Is a Netmask?

A netmask (or subnet mask) is a 32-bit value that separates the network portion of an IPv4 address from the host portion. It is commonly written in dotted-decimal format such as 255.255.255.0, or as a CIDR prefix like /24.

How CIDR and Subnet Masks Relate

/8 = 255.0.0.0
/16 = 255.255.0.0
/24 = 255.255.255.0
/30 = 255.255.255.252

CIDR is usually easier to read and appears in route tables and cloud dashboards, while dotted masks still appear in many device interfaces.

How to Use This Calculator

Type an IPv4 address (for example: 10.0.5.19).
Enter either a CIDR prefix (like 24) or subnet mask (like 255.255.255.0).
Click Calculate.
Review network, broadcast, host range, and host count results.

If you enter both CIDR and subnet mask, they must match. If they conflict, the calculator will show an error.

Key Outputs Explained

Network Address

This is the first address in the subnet and identifies the subnet itself. It cannot be assigned to a host in traditional subnets.

Broadcast Address

This is the last address in the subnet and is used to send traffic to all hosts in that subnet (for most IPv4 LAN contexts).

Usable Host Range

Usually, the usable range excludes network and broadcast addresses. For special cases:

/31: generally used for point-to-point links, both addresses are usable.
/32: represents a single host route.

Common Subnetting Pitfalls

Using a non-contiguous subnet mask (invalid in modern subnetting).
Mixing up network and host bits when writing ACLs.
Allocating overlapping private ranges in multi-site VPNs.
Forgetting that 172.16.0.0/12 is private, but 172.32.0.0 is not.

Practical Examples

Example 1: /24 Office LAN

IP: 192.168.10.57 with /24 gives: network 192.168.10.0, broadcast 192.168.10.255, and 254 usable hosts.

Example 2: /27 Small Segment

IP: 10.10.10.90 with /27 gives: network 10.10.10.64, broadcast 10.10.10.95, and 30 usable hosts.

Final Thoughts

Netmask math is one of those core networking skills that pays off every day. This calculator is designed to be fast, practical, and accurate for real-world IPv4 subnetting tasks. Keep it handy whenever you design new networks or troubleshoot existing ones.