Wildcard Mask Calculator
Instantly convert standard Subnet Masks or CIDR notation into Wildcard Masks. An essential tool for configuring Access Control Lists (ACLs) and routing protocols like OSPF.
Inverse Mask Converter
Valid mask required
Tip: The calculator works in real-time. Simply adjust the slider or type a mask to see the bitwise inversion instantly.
Wildcard Translation
Wildcard Mask
0.0.0.255
| Subnet Mask | 255.255.255.0 |
|---|---|
| Wildcard Mask | 0.0.0.255 |
| Binary Subnet Mask | 11111111.11111111.11111111.00000000 |
| Binary Wildcard Mask | 00000000.00000000.00000000.11111111 |
| Total IP Addresses | 256 |
How to Calculate a Wildcard Mask
A Wildcard Mask (often called an inverse mask) is the exact bitwise opposite of a Subnet Mask. Where a subnet mask uses binary 1s to lock down network bits, a wildcard mask uses binary 0s to match them.
- Select your Mask: Enter your standard Subnet Mask (e.g.,
255.255.255.0) or slide the CIDR bar to your desired prefix length. - View the Inversion: The tool instantly calculates the Wildcard Mask. Look at the Binary rows in the table to visually see how every
1in the Subnet Mask flips to a0in the Wildcard Mask. - Apply to Router: Copy the generated Wildcard Mask and paste it directly into your Cisco IOS Access Control List (ACL) or OSPF `network` statement.
The Subtraction Method
If you ever need to calculate a wildcard mask manually without a calculator, use the subtraction rule. Simply subtract your Subnet Mask from the global broadcast mask 255.255.255.255.
255 . 255 . 255 . 255
- 255 . 255 . 255 . 192 (Subnet Mask)
= 0 . 0 . 0 . 63 (Wildcard Mask)