Network Mask Calculator

Enter Network Values

IPv4 Address

CIDR Prefix

Dotted Subnet Mask

Required Hosts

Planned Reserved Hosts

Apply RFC 3021 rules for /31 point-to-point links

Tip: Enter either CIDR prefix or dotted mask. If both are entered, the dotted mask takes priority.

Example Data Table

IPv4 Address	CIDR	Subnet Mask	Network Address	Broadcast Address	Usable Hosts
192.168.10.25	/24	255.255.255.0	192.168.10.0	192.168.10.255	254
172.16.5.70	/26	255.255.255.192	172.16.5.64	172.16.5.127	62
10.0.12.200	/29	255.255.255.248	10.0.12.200	10.0.12.207	6

Formula Used

Subnet Mask from Prefix: Write the first p bits as 1 and the remaining bits as 0, where p is the CIDR prefix.
Network Address: Network = IP Address AND Subnet Mask.
Wildcard Mask: Wildcard = 255.255.255.255 - Subnet Mask.
Broadcast Address: Broadcast = Network Address OR Wildcard Mask.
Total Addresses: Total = 2^{(32 - prefix)}.
Usable Hosts: Usable = Total - 2 for most IPv4 subnets. Special handling applies to /31 and /32 networks.
Effective Usable Hosts: Effective = Standard Usable Hosts - Planned Reserved Hosts.
Smallest Recommended Subnet: Choose the smallest prefix whose usable capacity meets required hosts plus reserved hosts.

How to Use This Calculator

Enter the IPv4 address you want to evaluate.
Provide a CIDR prefix, or enter a dotted subnet mask.
Add required hosts to test whether the subnet fits your plan.
Add planned reserved hosts for gateways, growth, or infrastructure.
Enable RFC 3021 only for /31 point-to-point link planning.
Press the calculate button to view the network result above the form.
Review network, broadcast, wildcard, usable range, binary values, and the capacity graph.
Use the CSV or PDF buttons to export the final result.

FAQs

1. What does a network mask calculator do?

It converts a prefix or dotted mask into practical subnet details. You can see the network address, broadcast address, wildcard mask, host range, and total usable capacity from one calculation.

2. Why are subnet masks important in networking?

Subnet masks define which portion of an IPv4 address represents the network and which portion represents hosts. That separation controls routing, address planning, segmentation, and access design across your environment.

3. What is the difference between CIDR and subnet mask?

CIDR expresses the number of network bits as a prefix, such as /24. A subnet mask shows the same information in dotted decimal format, such as 255.255.255.0. They describe the same boundary in different forms.

4. Why are two IPv4 addresses usually unavailable?

In most IPv4 subnets, one address is reserved for the network itself and one for broadcast traffic. That is why usable host capacity is commonly total addresses minus two.

5. When should I use RFC 3021 for /31?

Use RFC 3021 on point-to-point links where only two endpoints need addressing. It allows both addresses in a /31 subnet to be usable, removing traditional network and broadcast reservations.

6. What is a wildcard mask?

A wildcard mask is the inverse of the subnet mask. It is often used in routing and access control lists because it highlights the host bits that may vary in an address match.

7. Can this calculator help with subnet planning?

Yes. The required hosts and reserved hosts inputs help test whether a subnet can support your design. The calculator also suggests a smallest-fit subnet for cleaner planning decisions.

8. Does this calculator support IPv6?

No. This version is focused on IPv4 network masks, host ranges, and broadcast calculations. IPv6 uses different addressing rules and would need a separate calculator workflow.