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CIDR Calculator

Calculate IPv4 CIDR ranges, subnet sizes, wildcard masks, and usable host boundaries with a fast subnetting workflow.

Live 3 calculations Network Tools Calculator Networking IPv4 Subnetting
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Input

Enter an IPv4 address and a CIDR prefix to calculate subnet boundaries, mask values, and usable host range.

Enter only the numeric prefix, for example 24 for /24.
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Result

Network boundaries, mask values, host counts, and binary subnet breakdown.

Input 198.51.100.10 /31
IP class C
Network bits 31
Host bits 1
Network address 198.51.100.10
Broadcast address 198.51.100.11
Subnet mask 255.255.255.254
Wildcard mask 0.0.0.1
Total addresses 2
Usable hosts 2
First usable host 198.51.100.10
Last usable host 198.51.100.11

What this means

The IPv4 address 198.51.100.10 belongs to the 198.51.100.10/31 network, and the subnet broadcast boundary is 198.51.100.11.

This subnet provides 2 total addresses and 2 usable host addresses, with a host range from 198.51.100.10 to 198.51.100.11.

The subnet mask is 255.255.255.254, the wildcard mask is 0.0.0.1, and the address falls into Class C.

Special case: /31 networks are typically used on point-to-point links, where both addresses can be treated as usable endpoints.

Common presets

192.168.1.10 /24 10.0.5.23 /16 172.16.10.200 /20 192.168.100.14 /27 203.0.113.9 /30 198.51.100.10 /31 203.0.113.44 /32

Binary breakdown

Inspect the binary representation of the IP, subnet mask, network, and broadcast values.

IP address

11000110.00110011.01100100.00001010

Subnet mask

11111111.11111111.11111111.11111110

Network address

11000110.00110011.01100100.00001010

Broadcast address

11000110.00110011.01100100.00001011

CIDR quick notes

Useful reminders for subnetting and host calculations.

/24 means 24 network bits and 8 host bits.

Subnet mask shows the network boundary, while wildcard mask is its inverse.

/31 is commonly used for point-to-point links, while /32 represents a single-host route.

CIDR quick reference

Common IPv4 subnet sizes for fast comparison without recalculating each time.

Prefix Subnet mask Total addresses Usable hosts
/16 255.255.0.0 65,536 65,534
/17 255.255.128.0 32,768 32,766
/18 255.255.192.0 16,384 16,382
/19 255.255.224.0 8,192 8,190
/20 255.255.240.0 4,096 4,094
/21 255.255.248.0 2,048 2,046
/22 255.255.252.0 1,024 1,022
/23 255.255.254.0 512 510
/24 255.255.255.0 256 254
/25 255.255.255.128 128 126
/26 255.255.255.192 64 62
/27 255.255.255.224 32 30
/28 255.255.255.240 16 14
/29 255.255.255.248 8 6
/30 255.255.255.252 4 2
/31 255.255.255.254 2 2
/32 255.255.255.255 1 1