Subnetting is the foundation of modern TCP/IP networking, cloud VPC routing, and network segmentation. Calculating IP masks, CIDR prefixes, wildcard masks, and usable host ranges by hand is time-consuming and error-prone. The 99tools Subnet Calculator provides an instant, interactive client-side calculator that breaks down network boundaries, broadcast addresses, and assignable IP blocks with zero latency and 100% in-browser computation.
CIDR & Netmask Conversion
Convert between standard decimal dotted netmasks (255.255.255.0) and CIDR bit prefixes (/8 to /32) instantly.
Host Range & Broadcast
Determine first usable IP, last usable IP, total usable client hosts, and reserved broadcast addresses automatically.
100% Client-Side Privacy
All IP arithmetic runs in your browser runtime. No private IP infrastructure or network architecture is ever logged or transmitted.
Common Subnet Classes & CIDR Reference Table
Reference guide for standard IPv4 network prefixes and host counts:
| CIDR Prefix | Subnet Mask | Total Addresses | Usable Hosts |
|---|---|---|---|
| /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 |