CIDR Calculator
Calculate the full subnet breakdown — network address, broadcast address, mask, and usable host range — from an IP address and CIDR prefix length.
- Free to use
- Accurate results
- No registration required
- Works on all devices
Enter an IP address and CIDR prefix (e.g. /28) to calculate the network address, broadcast address, subnet mask, and usable host range.
e.g. 10.0.0.1
Your result
10.0.0.0
Network address
Broadcast address10.0.0.15
Subnet mask255.255.255.240
First usable host10.0.0.1
Last usable host10.0.0.14
Usable host count14
AI explanation
Formula
CIDR /n means the first n bits of the 32-bit address are the network portion; mask = n leading 1-bits followed by (32−n) zero-bitsWorked example
10.0.0.1 / 28
| Field | Value |
|---|---|
| IP address | 10.0.0.1 |
| CIDR prefix (/n) | 28 |
| Network address | 10.0.0.0 |
| Broadcast address | 10.0.0.15 |
| Subnet mask | 255.255.255.240 |
| First usable host | 10.0.0.1 |
| Last usable host | 10.0.0.14 |
| Usable host count | 14 |
Assumptions
- IPv4 only.
- /31 networks follow RFC 3021 (2 usable point-to-point addresses); /32 is a single host route.
Frequently asked questions
What does the number after the slash mean in CIDR notation?
It's the prefix length — the number of leading bits (out of 32 for IPv4) that identify the network portion of the address, with the remaining bits available for host addresses.
How do I convert a CIDR prefix to a subnet mask?
Set the first n bits to 1 and the rest to 0, then group into 4 octets — e.g. /28 gives 11111111.11111111.11111111.11110000, or 255.255.255.240 in dotted-decimal.
Why use CIDR instead of separate subnet masks?
CIDR notation is more compact and enables "supernetting" — combining multiple smaller networks into a single larger routing entry, reducing the size of internet routing tables.