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CIDR Calculator

Calculate IP address ranges from CIDR notation. Convert between CIDR, subnet masks, and IP ranges. Essential for configuring SPF records and understanding IP allowlists.

CIDR Calculator

Calculate IP ranges from CIDR notation

CIDR Notation

192.168.1.0/24

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Network Address

192.168.1.0

Broadcast Address

192.168.1.255

First Usable Host

192.168.1.1

Last Usable Host

192.168.1.254

Subnet Mask

255.255.255.0

Wildcard Mask

0.0.0.255

Total IPs

256

Usable Hosts

254

SPF Record Format

ip4:192.168.1.0/24

Common CIDR Ranges

/32 = 1 IP (single host)

/30 = 4 IPs (point-to-point)

/24 = 256 IPs (Class C)

/16 = 65,536 IPs (Class B)

About this tool

CIDR notation is commonly used in email authentication to specify authorized IP addresses. This calculator helps you convert between CIDR notation and IP ranges, which is essential when configuring SPF records for your sending infrastructure. Once you've configured your SPF with proper CIDR ranges, verify it with our SPF checker and ensure all records have propagated using our DNS propagation checker.

Frequently Asked Questions

CIDR (Classless Inter-Domain Routing) notation represents IP ranges compactly. For example, 192.168.1.0/24 represents all IPs from 192.168.1.0 to 192.168.1.255 (256 addresses).

SPF records use CIDR notation to authorize IP ranges. For example, 'ip4:192.168.1.0/24' authorizes all 256 IPs in that range to send email for your domain.

The number (0-32 for IPv4) indicates how many bits are fixed. /32 is a single IP, /24 is 256 IPs, /16 is 65,536 IPs. Lower numbers mean larger ranges.

Count the number of 1s in the binary subnet mask. 255.255.255.0 = 11111111.11111111.11111111.00000000 = 24 ones = /24. Our calculator handles this conversion automatically.

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