Managed IT Services

Subnet Calculator and CIDR Notation Table

Subnet Calculator and CIDR Notation Table

SOC 2 Compliant
24/7 Support
30+ Years Experience

IP & Subnet Toolkit

Subnet Calculator and Quick Reference

IP & Subnet Toolkit

CIDR quick reference • Subnet calculator with tips • IP intake & class explanations

CIDR Notation Table (IPv4)

Quick reference for common prefixes.

PrefixSubnet MaskWildcardHosts / SubnetUsable HostsBlock Size (4th Octet*)

*Block size shown for the octet where subnetting occurs (typical /24+). For shorter prefixes, the block size applies to earlier octets.

Subnet Calculator

IPv4 address Mask or /Prefix Calculate FieldValue How to calculate manually (tips)

  • Convert /prefix → mask: /24 means 24 ones then 8 zeros → 11111111.11111111.11111111.00000000 → 255.255.255.0
  • Block size rule: In the first non-255 octet of the mask, do 256 − octet. Example: 255.255.255.192 ⇒ block size 256−192 = 64. Network ranges: ...0–63, 64–127, 128–191, 192–255.
  • Network address: bitwise AND of IP and mask. Example: 192.168.10.130 & 255.255.255.192 = 192.168.10.128
  • Broadcast address: all host bits set to 1. With /26 (64-block) starting at .128 ⇒ broadcast is .191
  • Usable hosts: 2^(32−prefix) − 2 (skip network & broadcast) — except /31 (2 point-to-point) and /32 (host).
  • First/Last usable: Network+1 and Broadcast−1 (for subnets where usable ≥2).

IP Intake & Classification

IPv4 address Optional /Prefix Analyze AttributeValue

Class explanations

  • Class A (0.0.0.0–127.255.255.255) — default mask /8. 10.0.0.0/8 is private. 127.0.0.0/8 is loopback.
  • Class B (128.0.0.0–191.255.255.255) — default mask /16. 172.16.0.0–172.31.255.255 is private.
  • Class C (192.0.0.0–223.255.255.255) — default mask /24. 192.168.0.0/16 is private.
  • Class D (224.0.0.0–239.255.255.255) — multicast (not host addressing).
  • Class E (240.0.0.0–255.255.255.255) — experimental.

We’ll also flag link-local (169.254.0.0/16), APIPA, loopback, and other special ranges when relevant.

Need Support? Click Below.

Initiate Your Upgrade

Let's Discuss Your IT Needs

Schedule a free consultation with our Houston IT experts. We serve businesses throughout the Greater Houston area including The Woodlands, Spring, Katy, and Sugar Land.

Reduce downtime and increase productivity
Enterprise-grade security protection
Predictable monthly IT costs
Expert support when you need it

Request a Free Quote

Get Free IT Assessment

Or call us directly at 888.792.8080