Network Tools

Subnet Calculator

Calculate CIDR subnet details like network, broadcast and host count.

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Enter IP address and CIDR to calculate subnet info

What is Subnet Calculator?

Subnet calculator computes network information from an IP address and subnet mask, including network address, broadcast address, and host range.

Calculated Information

  • Network address
  • Broadcast address
  • First and last usable host
  • Number of hosts
  • CIDR notation

Use Cases

  • Network planning
  • IP address allocation
  • Network troubleshooting

Frequently Asked Questions

What do /24 and /16 mean?
They count consecutive 1-bits in the subnet mask: /24 = 255.255.255.0 — 24 network bits, 8 host bits, 2⁸−2 = 254 usable hosts; /16 gives 65,534. Smaller prefix, bigger network.
Why is the usable host count always minus two?
Every subnet reserves two addresses: all-zero host bits is the network address itself, all-ones is broadcast. A /30 has just 2 usable — exactly why it serves point-to-point links. Exclude both from allocation planning.
How do I tell if two IPs share a subnet?
AND each IP with the mask; identical results mean same subnet. The intuition: 10.0.1.5 and 10.0.2.5 differ under /24 but match under /16 — when "ping fails without a gateway", compute this first.