IP Subnet Calculator
Plan networks and firewall rules with every subnet detail worked out for you.
- Your data never leaves your device
- 100% free
- No sign-up
- Works offline after first load
How to calculate a subnet
- Type an IP with a prefix or mask, like 192.168.1.10/24.
- Read the network, host range, masks and binary view.
- Split it into smaller subnets or check if an IP belongs to it.
About IP Subnet Calculator
Calculate IPv4 and IPv6 subnets.
Everything works in your browser, so it is instant and private, and your settings are remembered on this device.
Good for
- Planning networks and VLANs
- Firewall rules and cloud VPC design
- Studying for CCNA and network exams
Tip: Click a row in the prefix reference to try different subnet sizes quickly.
Frequently asked questions
How many hosts are in a /24?
256 addresses, 254 usable — the first is the network address and the last is the broadcast. /31 links have 2 usable addresses and /32 is a single host.
What is a wildcard mask?
The inverse of the subnet mask (0.0.0.255 for /24), used in Cisco ACLs and OSPF. It is shown for every network.
Does it support IPv6?
Yes — enter an address like 2001:db8::1/64 to see the network, first and last address, the number of addresses, the type and the reverse DNS name, and to split it into smaller subnets.
Can I convert an IP range to CIDR?
Yes — type a range such as 10.0.0.5 - 10.0.0.20 to get the smallest list of CIDR blocks that covers it exactly.
Is my data uploaded?
No. Everything is processed by JavaScript in your browser — nothing you paste or open is sent to a server, so it is safe for API responses, tokens, configs and customer data. It also works offline once the page has loaded.