IP Subnet Calculator
Calculate subnets, CIDR, and network ranges
| CIDR | Subnet Mask | Usable Hosts |
|---|---|---|
| /8 | 255.0.0.0 | 16,777,214 |
| /16 | 255.255.0.0 | 65,534 |
| /24 | 255.255.255.0 | 254 |
| /25 | 255.255.255.128 | 126 |
| /26 | 255.255.255.192 | 62 |
| /27 | 255.255.255.224 | 30 |
| /28 | 255.255.255.240 | 14 |
| /29 | 255.255.255.248 | 6 |
| /30 | 255.255.255.252 | 2 |
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IP Subnetting: Network Design and Address Planning
Key Takeaways
- Subnetting divides large IP networks into smaller, manageable segments — improving security, performance, and address utilization.
- CIDR notation (/24, /16, etc.) defines the network prefix length, determining how many hosts each subnet can accommodate.
- All subnet calculations are performed in your browser — your network architecture data stays private.
IP subnetting is a fundamental networking skill that enables efficient use of IP address space and logical network segmentation. Whether you are designing a corporate network, planning cloud VPC configurations, or troubleshooting connectivity issues, understanding subnet masks, CIDR notation, and address ranges is essential for every network engineer and cloud architect.
A /24 subnet provides 254 usable host addresses, while a /16 provides 65,534 — choosing correctly prevents address exhaustion.
Capacity Planning
Key Concepts
CIDR Notation
Classless Inter-Domain Routing (CIDR) notation like 192.168.1.0/24 specifies the network prefix length. The /24 means the first 24 bits are the network portion, leaving 8 bits (256 addresses) for hosts.
Subnet Mask
A subnet mask (e.g., 255.255.255.0 for /24) determines which bits of an IP address identify the network and which identify the host. ANDing an IP with its mask gives the network address.
Network, Broadcast, and Usable Addresses
Every subnet has a network address (first, all host bits 0), broadcast address (last, all host bits 1), and usable range (everything between). A /24 has 256 total addresses but only 254 usable.
VLSM — Variable Length Subnet Masking
VLSM allows different subnets within the same network to have different prefix lengths. This enables efficient address allocation — a /28 (14 hosts) for a small office and /22 (1022 hosts) for a data center.
Pro Tips
Always plan for growth — if you need 50 hosts now, use a /25 (126 hosts) or /24 (254 hosts) rather than a /26 (62 hosts).
Use private address ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) for internal networks to conserve public IPv4 addresses.
In cloud environments (AWS VPC, Azure VNet), remember that some addresses are reserved by the provider — typically the first 4 and last 1.
Document your subnet allocation plan — without documentation, overlapping subnets and routing conflicts are inevitable as networks grow.
All subnet calculations are performed entirely in your browser. Your network addressing information, which may reveal infrastructure details, is never transmitted to any server.