Wildcard Mask Converter
Convert ACL-style wildcard masks like 0.0.0.255 into subnet masks and CIDR notation.
Enter network values
Use the example or enter your own subnet, plan, MAC, or port value.
Results update locally in your browser.
Convert wildcard masks, often seen in ACL/networking contexts, into subnet masks and CIDR prefixes.
Wildcard mask explanation
Wildcard masks invert subnet-mask logic: 0 means “match this bit,” 1 means “ignore this bit.”
Equivalent to subnet mask 255.255.255.0 and prefix /24.
Capacity check shows whether the wildcard matches too broad or too narrow an address span.
permit ip 192.168.10.0 0.0.0.255 anynetwork 192.168.10.0 0.0.0.255 area 0
Copy output
Copies locally from this browser session only; CalcShelf does not save the value.
| Octet | Subnet mask bits | Wildcard bits |
|---|---|---|
| 1 | 11111111 | 00000000 |
| 2 | 11111111 | 00000000 |
| 3 | 11111111 | 00000000 |
| 4 | 00000000 | 11111111 |
| View | Value | How to read it |
|---|---|---|
| Subnet mask | 255.255.255.0 | 1 bits mark the network portion. |
| Wildcard mask | 0.0.0.255 | 0 bits must match; 1 bits are flexible. |
| Example matched range | 192.168.10.0 – 192.168.10.255 | Aligned example range this wildcard would match in ACL/OSPF syntax. |
| Address span | 256 | Number of addresses matched by this wildcard/prefix. |
| Option | CIDR | Mask | Wildcard | Total addresses | Usable hosts | Address change | Planning note |
|---|---|---|---|---|---|---|---|
| One size larger | /23 | 255.255.254.0 | 0.0.1.255 | 512 | 510 | +256 | Doubles the address span for more headroom. |
| Current size | /24 | 255.255.255.0 | 0.0.0.255 | 256 | 254 | — | Entered mask size. |
| One size smaller | /25 | 255.255.255.128 | 0.0.0.127 | 128 | 126 | -128 | Halves the address span for tighter segmentation. |
ACL notes
- Wildcard masks do not prove a firewall rule is safe; source, destination, service, and direction still matter.
- OSPF network statements select interfaces by address match, not remote networks to advertise directly.
- Non-contiguous wildcard masks exist in some ACL contexts, but CalcShelf intentionally converts standard CIDR-style contiguous masks.
Notes
These are planning and conversion utilities. Confirm production network changes against your router, firewall, cloud provider, and ISP requirements before applying them.
Get a better answer from the Wildcard Mask Converter
- Start with the example values to see how the tool behaves.
- Swap in your own numbers, even if they are rough first-pass estimates.
- Change one input at a time so you can see what actually moves the result.
What the result means
The result turns network notation into something easier to read: ranges, host counts, masks, wildcard masks, ports, or planning blocks.
How to use it
Use the output to plan or double-check, then compare it with the real network before changing a route, VLAN, DHCP scope, firewall rule, or ACL.
What can change it
A valid network number can still be wrong for your environment if it overlaps, conflicts with routing, exposes traffic, or breaks change-control rules.
Example to try
Convert the wildcard mask beside the subnet mask before pasting ACL or OSPF configuration so the inverted bits are explicit.
Assumption to challenge
Wildcard masks invert subnet masks in common Cisco-style contexts, but platform syntax and ACL match behavior still need vendor confirmation.
Verify next
Confirm source/destination direction, protocol, port, interface, route scope, deny/permit order, and change-control rollback.
Key terms
Wildcard bit
A 0 bit must match; a 1 bit can vary. This is why wildcard masks feel backwards compared with subnet masks.
ACL direction
Whether a rule is applied inbound or outbound on an interface can change what traffic it matches.
Common uses
- Convert ACL wildcard masks.
- Find matching subnet mask.
- Check CIDR prefix from wildcard.
Common questions
Is the Wildcard Mask Converter private?
Yes. CalcShelf calculators run without an account, do not save calculator entries, and do not put raw inputs into shareable URLs or analytics events.
How accurate is the Wildcard Mask Converter?
It follows common IPv4, CIDR, mask, range, and port conventions. Production networks still need live-config, routing, ACL, overlap, and change-control review.
What should I check after using the Wildcard Mask Converter?
Verify live allocations, overlaps, gateway conventions, routes, ACL/firewall order, documentation, and rollback plan before production changes.
Which calculator should I try next?
Use the related calculators below to cross-check the same decision from another angle before you act.
Method behind the estimate
Networking tools use IPv4, CIDR, subnet mask, wildcard mask, range, VLAN, DHCP, and port-reference rules for planning and sanity checks.
Why the detail matters
Before changing production routing, firewall, VLAN, DHCP, or address plans, verify against the actual network, documentation, and change-control process.
Privacy guardrail
Your calculator values are for you. CalcShelf does not require an account, save calculator entries, put your numbers into shareable URLs, or use raw inputs as analytics events.
Copy or print safely
Use any copy, print, or worksheet controls as local handoff tools for your own notes, supplier calls, lender questions, or implementation checklist. They are there to help you explain the result to a human.
Before acting
Treat the result as a decision draft, not a verdict. Recheck the source numbers, run a downside case, and verify the real-world rule, quote, label, or spec that controls the final answer.
Last reviewed: May 11, 2026. See methodology and editorial policy for formulas, assumptions, rounding, review approach, and limitations. For network changes, verify against live configuration, vendor docs, and change-control requirements.