What does /24 mean in CIDR notation?

In CIDR (Classless Inter-Domain Routing) notation, /24 means the subnet mask has 24 consecutive 1s (255.255.255.0), indicating 24 bits for the network portion and 8 bits for hosts. A /24 subnet can accommodate 254 usable host addresses (2^8-2), commonly used for small business or large home networks.

Why is the number of usable hosts 2^n - 2 instead of 2^n?

Each subnet reserves two addresses: the first address is the network address (all host bits 0) which identifies the network itself, and the last address is the broadcast address (all host bits 1) used to send packets to all hosts in the subnet. So the actual assignable host addresses are 2^n - 2. For example, a /24 subnet has 256 addresses but only 254 are usable.

How do I calculate subnets from a larger network?

Subnetting works by borrowing bits from the host portion. For example, to divide a /24 into 4 /26 subnets: borrow 2 bits from the 8 host bits (2^2=4 subnets), each getting 2^6-2=62 usable hosts. Subnet 1 covers 0-63 (network 0, broadcast 63), subnet 2 covers 64-127, and so on. This tool automatically calculates all subnets for any CIDR prefix — just input your network address and desired subnet count.

Can I use this tool on my mobile phone?

Yes, this subnet calculator is fully responsive and works on all devices including smartphones, tablets, and desktop computers. The interface adapts to your screen size automatically. All computations run locally on your device — no data is sent to any server, making it suitable for air-gapped and internal networks.

What is the difference between a subnet mask of 255.255.255.0 and 255.255.255.240?

255.255.255.0 is a /24 mask with 254 usable hosts, suitable for a small LAN. 255.255.255.240 is a /28 mask with only 14 usable hosts, used for smaller subnets. The trade-off is more subnets (16 subnets from a /24) at the cost of fewer hosts per subnet. Our tool can show you the exact breakdown for any mask value.

Free Subnet Calculator - Online CIDR IPv4 Subnetting Tool

📖 About Subnetting

Subnetting divides an IP network into smaller subnets to improve address utilization and network management. This tool supports:

CIDR Calculation: Enter IP + mask, get network/broadcast/host range instantly
Subnet Splitting: Automatically split a network into N equal subnets
Supernet Aggregation: Summarize multiple subnets into a single aggregate route
VLSM Support: Variable-Length Subnet Masks at any prefix length

Common Subnet Mask Reference

CIDR	Subnet Mask	Usable Hosts	Use Case
/30	255.255.255.252	2	Point-to-Point Link
/29	255.255.255.248	6	Small Network
/28	255.255.255.240	14	Small Subnet
/27	255.255.255.224	30	Small LAN
/26	255.255.255.192	62	Medium LAN
/24	255.255.255.0	254	Standard Class C
/23	255.255.254.0	510	Supernet
/22	255.255.252.0	1022	Supernet
/16	255.255.0.0	65534	Standard Class B

❓ Frequently Asked Questions

What is CIDR and why should I use it?

CIDR (Classless Inter-Domain Routing) replaced the traditional class-based IP addressing (A/B/C classes) with a flexible prefix-length notation. Instead of being limited to /8, /16, or /24 masks, you can use any prefix from /0 to /32. This allows much more efficient IP address allocation and enables VLSM (Variable Length Subnet Masking) and route aggregation, making it fundamental to modern internet routing.

Is this tool free to use?

Yes, this subnet calculator is completely free to use with no limitations, no registration required, and no ads. All calculations run locally in your browser using JavaScript — your IP addresses and network data never leave your device. You can use it offline and even in air-gapped or internal network environments.

What is VLSM (Variable Length Subnet Mask)?

VLSM allows using different subnet mask lengths within the same major network, enabling more flexible IP address allocation. For example, you could split a /24 into two /25 subnets (128 addresses each) and two /30 subnets (4 addresses each) for point-to-point links, rather than using equal-sized subnets. VLSM significantly improves address utilization and is widely used in enterprise networks.

How does supernetting reduce routing table size?

Supernetting (also called route summarization or aggregation) combines multiple contiguous subnets into a single, larger network. For example, instead of advertising four separate routes (192.168.0.0/24, 192.168.1.0/24, 192.168.2.0/24, 192.168.3.0/24), a router can advertise a single 192.168.0.0/22 route. This reduces routing table size, improves router performance, and increases network stability by minimizing route flapping.

How is the subnet calculator different from other IP tools?

Unlike many IP tools that require server-side processing or API calls, this subnet calculator runs entirely in your browser. There is no server upload, no API limits, and no data privacy concerns. It provides instant results for CIDR calculation, subnet splitting, and supernet aggregation in a single unified interface. It's designed for network engineers, IT administrators, students, and anyone studying for networking certifications like CCNA.

Subnet Calculator

📡 Enter IP Address / CIDR

📊 Results

🔍 Split Network into Subnets

🔗 Supernet / Route Summarization