Free tool
CIDR to IP Range Converter
Enter a CIDR block to see its network, broadcast, host range and total addresses. Advanced mode adds the netmask, wildcard and binary — and converts a start–end range back to CIDR.
How it works
- 1Enter a CIDR block (e.g. 203.0.113.0/24).
- 2We compute the network, broadcast, usable host range and count.
- 3Advanced: see netmask/wildcard/binary, or convert an IP range back to CIDR blocks.
Questions
Frequently asked
What is CIDR notation?
Classless Inter-Domain Routing notation (like 203.0.113.0/24) describes a block of IP addresses by a base address and prefix length — common in SPF records and IP allowlists.
Why does this matter for email?
SPF records and firewall/IP allowlists often use CIDR ranges. Converting between CIDR and explicit ranges helps you author and audit them correctly.
Can I check a whole list at once?
This free tool checks one at a time. To verify a full list — email, phone and company together — upload a CSV to BounceBlock and preview your first 100 rows free.
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