About Subnet Calculator (v2)

CIDR → subnet mask, network, broadcast, first/last host, host count. Part of the DevTools Surf developer suite. Browse more tools in the Networking collection.

Use Cases

• Plan network segmentation for cloud VPCs
• Verify a firewall rule covers the intended range
• Split a /16 into smaller subnets with exact host counts
• Teach CIDR math to engineers moving from bridged to routed networks

Tips

• Input format: 192.168.1.0/24
• /31 and /32 are supported for point-to-point links
• The wildcard mask is useful for ACL entries in Cisco IOS

Fun Facts

• The famous 10.0.0.0/8 'private' range reserves 16.7 million addresses per network — more than the entire public IPv4 internet had in 1985.
• CIDR (Classless Inter-Domain Routing) replaced the old Class A/B/C system in 1993 — without it, IPv4 addresses would have been exhausted by 2000.
• The /32 subnet mask assigns exactly one IP address. It's commonly used in cloud environments for host routes and loopback interfaces.

FAQ

What's new in v2?

Updated UI with live preview, wildcard mask output, and supernet splitting (start with a /16, divide into smaller /20s with host counts).

IPv4 only or IPv6 too?

Both. IPv6 subnetting follows the same math; the tool shows host counts in scientific notation for v6.

How many /24 subnets fit in a /16?

256. Each /24 has 256 addresses (254 hosts + network + broadcast). The tool's supernet mode shows the full breakdown.

What's a supernet vs subnet?

Subnet is a smaller piece of a larger network. Supernet is the larger parent. The tool can show both directions (split a supernet or combine subnets).