Results are provided for informational purposes only and may contain errors. Please verify important information independently. Use of this tool is at your own risk.
What the IPv4 Subnet Calculator does
The IPv4 Subnet Calculator takes an address in CIDR notation, such as 192.168.1.0/24, and works out the subnet it belongs to: the netmask, the network address, the broadcast address, the range of usable host addresses, the number of usable hosts and the total number of addresses in the block.
The number after the slash is the prefix length: how many of the 32 bits identify the network. A /24 leaves 8 bits for hosts, which gives 256 addresses, of which 254 can be assigned because the first is the network address and the last is the broadcast address. Every additional prefix bit halves the block. For /31 and /32 there is no separate usable range, since those are used for point-to-point links and single hosts. The calculation runs in your browser.
When to use it
- Planning a VPC in AWS, Azure or Google Cloud and splitting it into subnets.
- Writing a firewall rule or a security group that should match an exact address range.
- Checking whether two addresses are on the same subnet when troubleshooting a network.
- Studying for a networking exam such as CCNA, where subnetting is done by hand.
Worked example
Input
10.0.0.0/26Output
Netmask: 255.255.255.192
Network address: 10.0.0.0
Broadcast address: 10.0.0.63
Usable host range: 10.0.0.1 – 10.0.0.62
Usable hosts: 62
Total addresses: 64Common questions about the IPv4 Subnet Calculator
What if I enter an address in the middle of a block?
The calculator applies the mask to find the block it belongs to. 10.0.0.77/26 shows the network 10.0.0.64 and the broadcast 10.0.0.127, which is how you find a host's subnet.
Why do cloud providers give fewer usable hosts?
AWS, Azure and Google Cloud reserve a few extra addresses in each subnet for their router, DNS and future use. In an AWS /24 you can assign 251 addresses rather than 254.
Which ranges are private?
10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 are reserved for private networks (RFC 1918) and are not routed on the public internet. Home routers and cloud VPCs normally use them.
Does it support IPv6?
No, it handles IPv4 only. IPv6 subnetting follows the same prefix idea, but addresses are 128 bits long and a standard LAN subnet is a /64.
Is this tool free?
Yes, it's free to use. No signup, no email required. Get results on this page.
How do I get my result?
Use the tool on this page. Your result appears here; no email delivery is required.