Network Subnet Calculator
Calculate subnet masks, network addresses, broadcast addresses, and usable host ranges from CIDR notation, instantly in your browser. No account needed — works instantly in your browser.
IP Subnet Calculator
Quickly calculate network ranges, broadcast addresses, and usable hosts.
Enter a valid IP to see subnet details
What is a Network Subnet Calculator?
A network subnet calculator takes an IP address in CIDR notation — such as 192.168.1.0/24 — and computes the complete subnet breakdown: subnet mask, network address, broadcast address, first usable host, last usable host, and total usable host count. The /24 is the prefix length, indicating how many of the 32 bits in the IP address identify the network portion. The remaining bits identify individual hosts on that subnet.
This calculator runs entirely in your browser. No IP addresses or network configuration data are sent to any server — useful when working with internal or private IP ranges that should not leave your environment.
How to Use the Network Subnet Calculator
- Enter an IP address in CIDR notation — type an IP address followed by a slash and prefix length, such as
192.168.1.0/24, into the input field. - Review the subnet breakdown — the calculator instantly displays the subnet mask, network address, broadcast address, first host, last host, and total usable host count.
- Adjust the prefix length — change the
/24to another prefix (e.g./28or/16) to see how the subnet size and host count change in real time. - Copy or record the values — note the network address and broadcast address for use in firewall rules, routing tables, or cloud VPC configurations.
Understanding CIDR Notation
Classless Inter-Domain Routing (CIDR) notation is a compact way to represent an IP address and its subnet mask. Instead of writing 192.168.1.0 with a separate mask of 255.255.255.0, CIDR expresses both as 192.168.1.0/24. The prefix length after the slash tells you exactly how many bits are the network portion: /24 means 24 bits for the network, leaving 8 bits (256 addresses, 254 usable) for hosts. A /28 leaves only 4 bits for hosts (16 addresses, 14 usable).
Who Is This For?
- Network engineers configuring infrastructure who need to quickly verify subnet boundaries, host ranges, and broadcast addresses before applying firewall or routing rules.
- Developers working with cloud networking on AWS, GCP, or Azure who need to plan and validate CIDR blocks for VPCs, subnets, and security groups.
- Anyone studying for a networking certification (CCNA, CompTIA Network+) who needs to practice subnet calculations without doing binary arithmetic by hand.
Key Benefits
- Privacy — all calculations run in your browser; no IP addresses or network data are sent to a server.
- Free — no account, no subscription, no rate limits.
- No account required — enter a CIDR block and see results immediately.
- Complete subnet breakdown — network address, broadcast address, subnet mask, first host, last host, and usable host count all in one view.
Common Use Cases
Planning a VPC CIDR block before deploying a cloud infrastructure stack — verify that the range is large enough for current and projected host counts. Verifying that two subnet ranges do not overlap when designing a multi-tier network with separate subnets for web, application, and database layers. Calculating the correct subnet mask to enter into a router, firewall, or network interface configuration. Practicing subnet math for a networking exam without needing to convert between binary and decimal by hand.
Frequently Asked Questions
What is a subnet mask? ↓
A subnet mask is a 32-bit number that divides an IP address into network and host portions. A subnet mask of 255.255.255.0 means the first 24 bits identify the network and the last 8 bits identify the host — written in CIDR notation as /24. The subnet mask tells routers and devices which part of an IP address refers to the local network and which part refers to the individual device.
Is this subnet calculator free? ↓
Yes, completely free. All subnet calculations run in your browser — no server, no account, no limits. No IP addresses or network data leave your device.
What does /24 mean in networking? ↓
CIDR notation — the /24 means the first 24 bits of the IP address are the network portion. A /24 subnet has 256 total addresses, 254 usable hosts, and is the most common subnet size in small office and home networks. The remaining 8 bits (256 combinations) are used to address individual hosts on that subnet.
What is the difference between a network address and a broadcast address? ↓
The network address is the first address in a subnet — it identifies the subnet itself and cannot be assigned to a host. The broadcast address is the last address — packets sent to it reach all hosts on the subnet simultaneously. Both are unusable as individual host addresses, which is why a /24 has 254 usable hosts rather than 256.
Why are there always two unusable addresses in a subnet? ↓
Every IPv4 subnet reserves the first address as the network address and the last as the broadcast address. A /30 subnet, for example, has 4 total addresses but only 2 usable hosts — this is why /30 is commonly used for point-to-point links between two routers, where only two host addresses are needed.
How do I choose the right subnet size for a cloud VPC? ↓
Estimate the maximum number of hosts you will ever need, then add a buffer of at least 25–50% for future growth. A /24 gives 254 hosts, /23 gives 510, /22 gives 1022. Avoid using /16 or larger for individual subnets in production — it wastes address space and complicates routing. For AWS VPCs, note that AWS reserves the first 4 and last 1 address in every subnet, reducing usable host count by 5.
The tools and calculators provided on The Simple Toolbox are intended for educational and informational purposes only. They do not constitute financial, legal, tax, or professional advice. While we strive to keep calculations accurate, numbers are based on user inputs and standard assumptions that may not apply to your specific situation. Always consult with a certified professional (such as a CPA, financial advisor, or attorney) before making significant financial or business decisions.
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