Open the Subnet / CIDR Calculator
Enter an IPv4 address and CIDR prefix (like 192.168.1.0/24) to instantly get the subnet mask, network address, broadcast address.
- Free to use
- No signup
- Nothing to install
- Runs in your browser
Illustration. Open the tool for the real thing.
What is the Subnet / CIDR Calculator?
Enter any IPv4 address together with a CIDR prefix length (the /24 in 192.168.1.0/24) and this tool instantly computes everything that address block implies: the subnet mask in dotted-decimal form, the wildcard mask, the network address, the broadcast address, the first and last usable host addresses, and the total number of usable hosts in that subnet — all done with real binary bitmasking, not a lookup table.
This is the exact arithmetic a network engineer does by hand when planning IP address ranges, configuring a router or firewall, or troubleshooting why a device can't reach another one on the same network. Change the prefix length and watch every value update instantly, which makes it easy to compare how /24 versus /26 versus /28 actually divides up an address space.
3 steps to your result
Open the tool and follow along. Nothing to install.
What you get
Computes network, broadcast and usable range from actual bitwise AND/OR operations on the address.
Works for any CIDR notation, not just the common /24.
Shows exactly how many devices can live on the subnet and their first/last addresses.
The inverse mask used in ACLs and OSPF configuration, shown alongside the standard subnet mask.
AZRS tools are free to open and use.
It opens in your browser, so there is nothing to download.
Used for
Pick one to see how it fits.
Network and system administrators
Plan IP address ranges and verify subnet boundaries before configuring devices.
Try it freeStudents studying networking or CCNA material
Check subnetting homework and build real intuition for CIDR math.
Try it freeDevelopers setting up cloud VPCs
Work out how a /26 or /28 subnet divides within a larger /16 or /24 VPC block.
Try it freeHow it compares
A plain look at this tool next to the usual alternative.
| This utility | Desktop software | |
|---|---|---|
| Install | Nothing to install | Usually an app or program to install |
| Account | No signup | Depends on the product |
| Cost | Free to use | Free or paid, depends on the product |
| Where it runs | In your browser tab | On your computer |
Questions people ask
What does /24 mean?
It means the first 24 bits of the 32-bit IPv4 address are the fixed network portion, leaving 8 bits (256 addresses, 254 usable) for hosts — equivalent to a 255.255.255.0 subnet mask.
How many usable hosts does a subnet have?
Usually 2^(32-prefix) minus 2 (for the network and broadcast addresses), except /31 (2 usable, no broadcast) and /32 (1 usable, a single host).
What is a wildcard mask?
The bitwise inverse of the subnet mask, used in access control lists and some routing protocol configuration — this tool shows it alongside the standard mask.
What is the difference between the network address and the first usable address?
The network address (e.g. 192.168.1.0) identifies the subnet itself and can't be assigned to a device; the first usable address (192.168.1.1) is the lowest address a device can actually use.
Does this work for IPv6?
No, this calculator is IPv4-specific; IPv6 subnetting uses a different, much larger address space and different conventions.
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Try the Subnet / CIDR Calculator now
Enter an IP and CIDR prefix to get network address, broadcast address, usable range and. Free to use.
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