How to use the CIDR to IP Range Calculator
- 1. Type a CIDRFor example 10.0.0.0/16 or 192.168.1.10/27. An IP plus netmask works too.
- 2. CalculateSee the network, broadcast, host range and masks.
- 3. Plan subnetsUse the next-network line to lay out blocks without overlaps.
Worked example: 192.168.1.0/24
The default 192.168.1.0/24 gives a usable range of 192.168.1.1 – 192.168.1.254. The /24 means the first 24 bits are the network part, leaving 8 bits, or 256 addresses. The first, 192.168.1.0, is the network address and the last, 192.168.1.255, is the broadcast, so 254 hosts can be assigned. The netmask is 255.255.255.0 and the wildcard mask, used in Cisco ACLs and some firewalls, is 0.0.0.255.
In an AWS VPC the same block holds 251 usable addresses, because AWS reserves five in every subnet: the network address, the VPC router, DNS, one for future use and the last address.
Quick reference and edge cases
- /32 is a single host and /31 is a point-to-point link where both addresses are usable (RFC 3021).
- /16 has 65,536 addresses, /20 has 4,096, /26 has 64, /28 has 16.
- Private ranges from RFC 1918 are 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16; the tool labels them.
- If you type a host address such as 172.16.5.4/27, the tool shows the network it belongs to, 172.16.5.0/27.
When planning a VPC, leave room to grow: a /16 split into /20 subnets gives sixteen blocks of 4,096 addresses, one per Availability Zone and tier. The calculator works on IPv4 only. For IPv6 address forms, use the IPv6 expander and compressor, and look up what runs on common ports with the port numbers reference.
Frequently asked questions
What does the number after the slash mean?
It is the prefix length: how many leading bits are fixed as the network. Bigger numbers mean smaller networks.
Can a netmask like 255.255.0.255 be written as CIDR?
No. CIDR masks are a run of 1 bits followed by 0 bits. The tool tells you when a mask is not contiguous.
Is the CIDR to IP Range Calculator free?
Yes, the CIDR to IP Range Calculator is free. The first time you see your first result, you are asked for your name and WhatsApp number once. After that, this and every other Uncodemy tool opens straight away without the form.