Wildcard Mask Calculator

Convert between subnet masks and wildcard masks for Cisco ACL configuration. Includes ACL examples and a quick reference table.

Try Wildcard Mask Calculator →

What It Does

The Wildcard Mask Calculator converts between subnet masks and wildcard masks — the inverse notation used by Cisco IOS for access control lists (ACLs) and OSPF network statements. It outputs both masks, the CIDR prefix, host counts, binary representations, and a ready-to-paste Cisco ACL example.

How to Use It

Navigate to IP Tools → Wildcard Mask from the top menu.
Choose your input mode using the tabs at the top: Subnet Mask → Wildcard, Wildcard → Subnet Mask, or CIDR → Both.
Enter the value in the input field.
Click Convert or press Enter.
View the results including the Cisco ACL example at the bottom.
Use Copy All or Download .txt to export.

Three Input Modes

Subnet Mask → Wildcard: Enter a subnet mask like 255.255.255.192 to get the wildcard 0.0.0.63.
Wildcard → Subnet Mask: Enter a wildcard like 0.0.0.15 to get the subnet mask 255.255.255.240.
CIDR → Both: Enter a prefix length like 27 to get both the subnet mask and wildcard mask.

Example: Creating a Cisco ACL

You need to permit traffic from the 192.168.10.0/26 network:

Select Subnet Mask → Wildcard mode.
Enter 255.255.255.192.
Click Convert.
The ACL example shows: permit ip 192.168.1.0 0.0.0.63
Copy and adapt for your specific ACL entry.

Reference Table

The reference table at the bottom shows the most commonly used CIDR prefixes with their subnet mask, wildcard mask, usable host count, and a sample ACL snippet — all in one glance.

Use Cases

Cisco ACLs: Get the exact wildcard mask for access-list entries.
OSPF configuration: Network statements require wildcard masks.
Quick reference: Look up mask conversions without manual binary math.
Documentation: Export for network change tickets and runbooks.