Subnet Calculator

Quick Answer

Last updated: 3 November 2026 ·How we calculate this: binary AND of the address and the subnet mask

How This Subnet Calculator Works

Enter an IPv4 address and choose a prefix length, or type the address in CIDR form such as 10.0.5.20/22. The calculator turns the address and mask into 32-bit numbers, keeps the network bits with a binary AND, and sets all host bits to 1 for the broadcast address. It then lists the usable host range, host count, wildcard mask, address type and a binary view.

How to Use the Subnet Calculator

1. Enter an IPv4 address, or an address with /prefix.
2. Choose the prefix length or subnet mask.
3. Press Calculate.
4. Read the network, broadcast and usable host range.
5. Check the binary view to see the network and host bits.

Core Formulas

• Network: IP AND mask
• Broadcast: network OR (NOT mask)
• Total addresses: 2^{(32 − prefix)}
• Usable hosts: 2^{(32 − prefix)} − 2, for prefixes up to /30
• Wildcard mask: 255.255.255.255 − subnet mask

Key Terms

• Subnet: a smaller network made by splitting a larger IP range.
• CIDR: Classless Inter-Domain Routing, the /prefix way of writing a network.
• Subnet mask: a 32-bit number with 1s for the network part of an address.
• Broadcast address: the last address in a subnet, used to reach all hosts.
• Usable host: an address that can be given to a device.

Worked Example

Find the subnet for 10.0.5.20/22.

• Mask: /22 = 255.255.252.0, so the third octet steps by 4
• 5 falls in the block 4–7, so the network is 10.0.4.0 and the broadcast is 10.0.7.255
• Usable hosts: 10.0.4.1 to 10.0.7.254, which is 1,022 hosts

Real-Life Examples

• Home networks: 192.168.1.0/24 gives 254 devices.
• Office VLANs: split a /24 into four /26 subnets of 62 hosts each.
• Cloud networks: plan VPC and subnet CIDR blocks without overlaps.
• Firewall rules: wildcard masks, such as 0.0.0.63 for /26, are used in many access lists.

Subnet Mask vs Wildcard Mask

• Subnet mask: 1s for network bits, such as 255.255.255.0.
• Wildcard mask: the opposite, 1s for host bits, such as 0.0.0.255.
• Use: masks set up interfaces, while wildcard masks are used in many router access lists and routing settings.

Subnet Mask Cheat Sheet

Tips for Subnetting

• Block size: 256 minus the interesting mask octet, such as 256 − 192 = 64 for /26.
• Private ranges: 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 are for internal networks.
• Point-to-point links: /31 gives two usable addresses with no broadcast.
• Plan for growth: leave spare addresses in each subnet.

To check a subnet in your head, find the octet where the mask is not 255 or 0 and work out the block size. For /26, the last octet of the mask is 192, so the block size is 64 and subnets start at 0, 64, 128 and 192. An address ending in .130 falls in the block that starts at 128, so its network is .128 and its broadcast is .191, one less than the next block.

Common Mistakes to Avoid

• Using the network or broadcast address for a device. They are not usable for hosts in normal subnets.
• Forgetting the −2. A /24 has 256 addresses but 254 usable hosts.
• Overlapping subnets. 10.0.0.0/23 already includes 10.0.1.0/24.
• Mixing up mask and wildcard. 255.255.255.0 and 0.0.0.255 are opposites.
• Picking subnets too small. Leave room for growth.

Frequently Asked Questions

References & Sources