IP Subnet Calculator
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Free IP Subnet Calculator — CIDR, Network & Host Range (2026)
Every device on a network needs an IP address. Subnetting is the practice of dividing a large IP address space into smaller, manageable chunks — each with its own network address, broadcast address, and range of usable host addresses. Getting this wrong means misconfigured networks, security gaps, and connectivity failures.
SmallSEOToolsn’s free IP subnet calculator takes any IP address and subnet mask (or CIDR notation) and instantly returns the network address, broadcast address, usable host range, and total host count.
KEY TAKEAWAYS
- Subnetting divides a large IP network into smaller subnetworks for security, efficiency, and management.
- CIDR notation (e.g., 192.168.1.0/24) specifies both IP address and subnet mask in one expression.
- /24 subnet has 256 addresses, 254 usable hosts. /16 has 65,536 addresses, 65,534 usable.
- Network address (first IP) and broadcast address (last IP) cannot be assigned to hosts.
- Used by network engineers, sysadmins, and anyone configuring routers, firewalls, or cloud VPCs.
Understanding IP Addresses and Subnet Masks
An IPv4 address is 32 bits written as four octets: 192.168.1.75
A subnet mask defines which part is the network and which is the host:
- 255.255.255.0 = /24 CIDR = first 24 bits are network, last 8 bits are hosts
CIDR Notation: 192.168.1.75 /24 means:
- Network address: 192.168.1.0
- Broadcast address: 192.168.1.255
- Usable hosts: 192.168.1.1 → 192.168.1.254 (254 hosts)
Common Subnet Reference Table
| CIDR | Subnet Mask | Total IPs | Usable Hosts | Typical Use |
|---|---|---|---|---|
| /8 | 255.0.0.0 | 16,777,216 | 16,777,214 | Large ISP/enterprise |
| /16 | 255.255.0.0 | 65,536 | 65,534 | Large LAN |
| /24 | 255.255.255.0 | 256 | 254 | Small office LAN |
| /25 | 255.255.255.128 | 128 | 126 | Medium dept |
| /26 | 255.255.255.192 | 64 | 62 | Small dept |
| /27 | 255.255.255.224 | 32 | 30 | Small team |
| /28 | 255.255.255.240 | 16 | 14 | Very small subnet |
| /30 | 255.255.255.252 | 4 | 2 | Point-to-point links |
| /32 | 255.255.255.255 | 1 | 0 | Single host route |
How to Calculate Subnets Manually
- Convert IP to binary: 192.168.1.75 →
11000000.10101000.00000001.01001011 - Apply subnet mask: 255.255.255.0 →
11111111.11111111.11111111.00000000 - Network address: AND the IP with mask →
11000000.10101000.00000001.00000000= 192.168.1.0 - Broadcast: Fill host bits with 1s →
11000000.10101000.00000001.11111111= 192.168.1.255 - Usable range: Network + 1 → Broadcast − 1 = 192.168.1.1 → 192.168.1.254
AWS / Azure / GCP Cloud Networking Context
Cloud VPC (Virtual Private Cloud) configurations require subnet calculations constantly. Typical VPC setup:
- VPC CIDR: 10.0.0.0/16 (65,534 usable IPs)
- Public subnet: 10.0.1.0/24 (254 hosts, internet-accessible)
- Private subnet: 10.0.2.0/24 (254 hosts, internal only)
- Database subnet: 10.0.3.0/24 (254 hosts, no internet access)
SmallSEOToolsn’s subnet calculator helps plan these VPC architectures before provisioning.
AI Overview Answer
How does an IP subnet calculator work? An IP subnet calculator takes an IP address and subnet mask (or CIDR notation like /24) and computes: network address (AND of IP and mask), broadcast address (network with all host bits set to 1), usable host range (network+1 to broadcast-1), and total usable host count (2^(32-prefix) − 2). Example: 192.168.1.75/24 gives network 192.168.1.0, broadcast 192.168.1.255, 254 usable hosts.
FAQs
Q: How many hosts can a /24 subnet support? A: 256 total IPs minus 2 (network and broadcast) = 254 usable host addresses.
Q: What is CIDR notation? A: CIDR (Classless Inter-Domain Routing) notation combines IP address and prefix length: 192.168.1.0/24. The /24 means the first 24 bits are the network portion, leaving 8 bits for hosts.
Q: Why can’t I use the first and last IP in a subnet? A: The first IP is the network address (identifies the subnet itself). The last IP is the broadcast address (packets sent here reach all hosts in the subnet). Neither can be assigned to a device.
→ Enter your IP address and subnet mask above to calculate instantly.
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