Subnet mask--
Total addresses--
Usable hosts--
CIDR to Subnet Mask Converter
Convert CIDR prefixes like /24, /27, or /30 into subnet masks and host counts for everyday IPv4 network planning.
Updated May 2026No signup requiredBuilt for mobile
Formula or method
CIDR prefix = number of network bits.
Host bits = 32 - prefix.
Total addresses = 2 raised to host bits.
Worked examples
Common LAN
/24 converts to 255.255.255.0 with 256 total addresses and 254 traditional usable hosts.
Small subnet
/30 converts to 255.255.255.252 with 4 total addresses and 2 traditional usable hosts.
Practical use cases
- network documentation
- VLAN design
- DHCP planning
- firewall planning
- router configuration
Common mistakes
- Forgetting the slash
- counting network and broadcast as hosts on ordinary LANs
- using classful shortcuts
- not checking overlap
FAQ
CIDR to Subnet Mask Converter questions
How accurate is this calculator?
It is a planning estimate based on the values you enter. Real-world conditions can change the result.
Why do results vary?
Overhead, rounding, equipment limits, supplier units, network conditions, and user behavior can all affect the final number.
Should I round up?
Round conservatively when running short would interrupt a project, backup, stream, trip, or outage plan.
What should I do next?
Use the result card and checklist, then compare related calculators or guides before making a final decision.
Does this replace official documentation?
No. Use manufacturer documentation, platform guidance, or professional advice for critical decisions.