🌐 IP & CIDR Subnet Calculator (IPv4 & IPv6)

Using IP / CIDR Subnet Calculator

Work out the network address, usable host range and mask of an IPv4 or IPv6 subnet when configuring a router, firewall rule or cloud VPC.

How to use it

1. Type an address with its prefix, such as 192.168.10.37/26, or click a preset like IPv4 /24 or IPv6 /64.
2. Read the network and broadcast addresses in the Subnet Breakdown.
3. Check the first and last usable host and the number of usable hosts before assigning addresses.
4. Copy the breakdown for your notes or change ticket.

Worked example

Input and settings

192.168.10.37/26

Expected result

Network 192.168.10.0; broadcast 192.168.10.63; hosts 192.168.10.1–192.168.10.62 (62 usable); mask 255.255.255.192; private range.

Limits and common mistakes

• This is arithmetic only; it does not ping, scan or check whether an address is in use.
• Cloud providers reserve extra addresses in each subnet (AWS keeps five), so your usable count is lower there.
• IPv6 has no broadcast address; the breakdown shows the first and last address and the total count instead.
• /31 and /32 IPv4 prefixes are special cases for point-to-point links and single hosts.

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