🌐 CIDR Subnet Calculator
Calculate network address, subnet mask, host range and more from CIDR notation
192.168.1.0192.168.1.255255.255.255.00.0.0.255192.168.1.1192.168.1.254254Class CYes (RFC 1918)How to Use the CIDR Calculator
Enter an IP address with CIDR prefix length (e.g. 10.0.0.0/8 or 192.168.1.100/24). The calculator computes: network address (first address), broadcast (last address), subnet mask, wildcard mask, first/last usable host addresses, and total hosts. Common subnets: /8 = 16M hosts (Class A), /16 = 65534 hosts, /24 = 254 hosts, /30 = 2 hosts (point-to-point links), /32 = single host.
What does the /24 mean in a CIDR block like 192.168.1.0/24?
The /24 is the prefix length — the first 24 of 32 bits are the network portion, the remaining 8 bits are for hosts. /24 leaves 8 bits for hosts: 2^8 = 256 addresses, of which 254 are usable (first is network address, last is broadcast). Common prefix lengths: /32 = single host, /30 = 2 usable hosts (point-to-point links), /29 = 6, /28 = 14, /27 = 30, /26 = 62, /25 = 126, /24 = 254, /23 = 510, /16 = 65,534.
How do I choose the right CIDR block size for an AWS VPC?
AWS recommends between /16 (65,536 IPs) and /28 (16 IPs). For a typical production VPC, /16 gives most flexibility. AWS reserves the first 4 IP addresses and last 1 in every subnet, so a /24 subnet has 251 usable addresses. Standard pattern for /16 VPC: create /24 subnets per availability zone per tier. Avoid using 10.0.0.0/8 for the entire VPC — you cannot peer with networks in that same range later.
What are the private IP address ranges?
RFC 1918 defines three private ranges not routable on the public internet: 10.0.0.0/8 (16.7 million addresses — preferred for large enterprise networks and VPCs), 172.16.0.0/12 (1 million — often used for Docker and container networking), 192.168.0.0/16 (65,536 — standard for home and small office networks). All cloud VPCs, office networks, and container networks should use one of these. When two networks need to communicate via VPN or peering, their CIDR blocks must not overlap.
How do I split a /24 network into smaller subnets?
Each additional bit added to the prefix length halves the addresses. A /24 (256 IPs) can split into: 2x /25 (128 IPs each), 4x /26 (64 each), 8x /27 (32 each), 16x /28 (16 each). To split 192.168.1.0/24 into four /26 subnets: 192.168.1.0/26 (.0–.63), 192.168.1.64/26 (.64–.127), 192.168.1.128/26 (.128–.191), 192.168.1.192/26 (.192–.255). This calculator outputs all values automatically.
What is the difference between a subnet mask and CIDR prefix length?
They represent the same information in different formats. /24 CIDR = subnet mask 255.255.255.0. /16 = 255.255.0.0. The mask ANDs with an IP address to extract the network portion: 192.168.1.100 AND 255.255.255.0 = 192.168.1.0 (the network address). CIDR notation (/24) is more compact and universally used in routing tables, firewall rules, and cloud configuration. Subnet mask notation still appears in older network device configuration interfaces.
How do I check if two IP addresses are in the same subnet?
AND both IPs with the subnet mask and compare. If results are equal, both are in the same subnet. Example: Is 10.0.1.50 in the same /24 as 10.0.1.200? 10.0.1.50 AND 255.255.255.0 = 10.0.1.0. 10.0.1.200 AND 255.255.255.0 = 10.0.1.0. Same result — yes, same /24. Is 10.0.1.50 in the same /25 (mask 255.255.255.128) as 10.0.1.200? 50 AND 128 = 0, 200 AND 128 = 128 — different subnets.
What other network tools are on this site?
The IP Subnet Calculator provides VLSM planning for networks requiring subnets of different sizes. The chmod Calculator handles Unix file permissions — another common infrastructure calculation involving bit operations. The Bandwidth Calculator estimates file transfer times and throughput. The HTTP Status Codes reference covers API gateway and load balancer error codes. All are in the Dev Tools Network section.
📊 Key Data Points
/24 = 254 hosts
Most common subnet size — 256 addresses minus network and broadcast
/16 = 65534 hosts
Typical AWS VPC size — large enough for most production environments
2^(32-n)
Formula for total addresses in a CIDR block where n is the prefix length
CIDR Calculator — IP Subnet Calculator -- Complete USA Guide 2026
CIDR notation expresses IP address ranges as a base address plus a prefix length — 192.168.1.0/24 means the first 24 bits are the network, leaving 8 bits for 254 host addresses. Getting subnet sizes wrong wastes IP space in VPCs or leaves no room for future hosts.
This calculator converts CIDR blocks to IP ranges, subnet masks, broadcast addresses, and usable host counts. Runs in your browser.
**Long-tail searches answered here:** what IP range does 10.0.0.0/16 cover, how many hosts in a /24 subnet, AWS VPC CIDR block calculator free online.
For network infrastructure setup, pair with IP Subnet Calculator.
🔬 How This Calculator Works
A CIDR prefix length (the number after /) determines the subnet mask. /24 = 255.255.255.0, /16 = 255.255.0.0, /8 = 255.0.0.0. The network address is the base IP ANDed with the subnet mask. The broadcast address is the network address ORed with the inverted mask.
Usable hosts = 2^(32 - prefix_length) - 2 (subtracting network address and broadcast address). A /24 has 256 addresses - 2 = 254 usable hosts. A /32 is a single host. A /0 is the entire IPv4 space.
✅ What You Can Calculate
IP range from CIDR
Enter 192.168.10.0/24 and instantly see the range is 192.168.10.0 to 192.168.10.255 with 254 usable hosts. No mental math required.
Usable host count
Accounts for the reserved network and broadcast addresses — shows usable hosts, not just total addresses. Avoids the off-by-two error that breaks DHCP configurations.
Subnet mask conversion
Converts between prefix length notation (/24) and dotted-decimal subnet masks (255.255.255.0) — both forms are needed depending on your router, firewall, or cloud console.
IP-in-range check
Enter any IP address and CIDR block to check whether the IP falls within the range. Useful for verifying firewall rules and security group configurations.
🎯 Real Scenarios & Use Cases
AWS VPC planning
AWS recommends /16 VPCs with /24 subnets per availability zone per tier. Calculate here to plan your address space before creating the VPC — you cannot resize it after creation.
Kubernetes cluster networking
Kubernetes needs non-overlapping CIDR blocks for pods and services. Calculate your pod CIDR (/16) and service CIDR (/12) here to ensure they do not overlap with your node network.
Firewall rule verification
Your security group allows traffic from 10.0.0.0/8. Use the IP-in-range check to verify whether a specific IP address would match this rule.
Network segmentation design
Divide a /16 into /24 subnets for different environments (dev, staging, prod). Calculate here to ensure no overlap before applying to your network infrastructure.
💡 Pro Tips for Accurate Results
AWS reserves 5 IPs per subnet. AWS reserves the first 4 IP addresses and the last 1 in every subnet — so a /24 has 251 usable IPs in AWS, not 254. Plan your subnet sizes accordingly.
Never use 10.0.0.0/8 for your VPC. Using the entire /8 prevents VPC peering with any other network in the 10.x.x.x range later. Use /16 or /18 instead.
Avoid 169.254.x.x. This range is reserved for link-local addresses — conflicts with EC2 instance metadata and APIPA addresses.
Plan for growth. Allocate more IP space than you currently need — a /22 (1,024 IPs) costs the same as a /24 (256 IPs) in AWS and gives you room to grow.
🔗 Use These Together
🏁 Bottom Line
CIDR notation is compact notation with non-obvious arithmetic. Getting the subnet size wrong in a cloud VPC or Kubernetes cluster creates networking problems that are expensive to fix after deployment.
For complete network planning: calculate subnets here, check connectivity with API Response Time, and measure throughput with Bandwidth Calculator.