IP Class Finder
Determine the class (A, B, C, D, or E) of any IPv4 address from its first octet. Classful addressing is largely superseded by CIDR but is still used in education and legacy docs. Runs in your browser.
Find IP Class
Enter any IPv4 address and click Get class to see its classful class (A–E), default mask, and default prefix.
Result
| IP address | 192.168.1.1 |
|---|---|
| Class | Class C |
| First octet | 192 |
| Default subnet mask | 255.255.255.0 |
| Default prefix (CIDR) | /24 |
| Description | Class C. Small networks; default /24. |
What Are IP Address Classes?
In classful addressing, IPv4 was divided into five classes by the leading bits of the first octet. Class A (0): first octet 1–126, default /8. Class B (10): 128–191, default /16. Class C (110): 192–223, default /24. Class D (1110): 224–239, multicast. Class E (1111): 240–255, reserved. This scheme was rigid and wasted address space; CIDR (classless) replaced it with variable-length prefixes. Classes are still useful for quick reference and learning.
To find the class of an IP, look at the first octet. 10.0.0.1 is Class A; 172.16.0.1 is Class B; 192.168.1.1 is Class C. Our IP address validator confirms whether an address is valid IPv4 or IPv6. The private vs public IP checker tells you if an address is in a private range (e.g. 10.x, 172.16–31.x, 192.168.x). For subnet math use the subnet calculator and CIDR calculator.
Class Default Masks and Ranges
Class A default mask 255.0.0.0 (/8); Class B 255.255.0.0 (/16); Class C 255.255.255.0 (/24). In practice, networks are subnetted with CIDR (e.g. a Class C range might be split into /25 or /28). Our subnet calculator works with any CIDR. The network address calculator and broadcast address calculator give the first and last address of a subnet. For host count see IP block size calculator.
Why Class Still Matters
Legacy configs, documentation, and certifications still reference classes. Knowing the class helps you quickly estimate the size of a block (A: huge, B: large, C: small). For real design work use CIDR and our IP range calculator and IP range generator. For geolocation use IP lookup; for connectivity use ping test and traceroute.
FAQs
What are IP address classes?
Classful addressing (A, B, C, D, E) divided IPv4 by leading bits. Class A: 0xxx (/8), B: 10xx (/16), C: 110x (/24). Largely replaced by CIDR but still referenced.
How do I find the class of an IP?
Look at the first octet. 1–126: A, 128–191: B, 192–223: C, 224–239: D (multicast), 240–255: E. Or use our IP address validator and check the range.
Are IP classes still used?
CIDR replaced classful addressing for routing. Classes are still taught and appear in legacy docs; modern design uses CIDR and subnet masks.
What is the default mask for Class B?
Class B default subnet mask is 255.255.0.0 (/16). First two octets are network, last two are host.