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IP Subnet Calculator

Calculate subnets with CIDR notation. Get network address, broadcast address, usable host count, and subnet masks instantly. Perfect for network engineers and system administrators.

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IP Address

Enter any IP address within the subnet

CIDR Prefix

Network prefix length (8-32)

CIDR Quick Reference

Common CIDR notations with subnet masks and host counts

CIDR	Subnet Mask	Wildcard Mask	Total Hosts	Usable Hosts	Description
/8	255.0.0.0	0.255.255.255	16,777,216	16,777,214	Class A network
/16	255.255.0.0	0.0.255.255	65,536	65,534	Class B network
/24	255.255.255.0	0.0.0.255	256	254	Class C network (most common)
/25	255.255.255.128	0.0.0.127	128	126	Half of /24
/26	255.255.255.192	0.0.0.63	64	62	Quarter of /24
/27	255.255.255.224	0.0.0.31	32	30	Small office network
/28	255.255.255.240	0.0.0.15	16	14	Very small network
/29	255.255.255.248	0.0.0.7	8	6	Tiny network
/30	255.255.255.252	0.0.0.3	4	2	Point-to-point link
/31	255.255.255.254	0.0.0.1	2	2	RFC 3021 point-to-point
/32	255.255.255.255	0.0.0.0	1	1	Single host

Understanding CIDR Notation: /24 = 254 usable hosts (most common) · /30 = 2 hosts (point-to-point) · /32 = 1 host (single IP)

Understanding Subnetting

Learn the basics of IP networking, subnetting, and addressing to better manage your networks.

What is Subnetting?

Subnetting is the practice of dividing a network into two or more smaller networks. It helps improve network performance and security by reducing broadcast traffic and organizing hosts into logical groups.

Understanding CIDR

Classless Inter-Domain Routing (CIDR) is a method for allocating IP addresses and IP routing. It uses a suffix (e.g., /24) to indicate the number of bits used for the network prefix, replacing the older class-based system.

Private vs Public IPs

Private IP addresses (RFC 1918) are used within local networks and are not routable on the internet. Public IP addresses are assigned by ISPs and are unique across the entire internet.

IPv4 vs IPv6

IPv4 uses 32-bit addresses (approx 4.3 billion addresses), while IPv6 uses 128-bit addresses (virtually infinite). IPv6 was developed to solve the IPv4 address exhaustion problem.

Subnet Masks

A subnet mask is a 32-bit number that masks an IP address, and divides the IP address into network address and host address. It distinguishes the network portion from the host portion.

Broadcast Address

The last address in a subnet is reserved as the broadcast address. It allows sending data to all devices on that specific subnet simultaneously. It cannot be assigned to a specific host.

Frequently Asked Questions

Common questions about subnet calculations and IP addressing

What is CIDR notation?

CIDR (Classless Inter-Domain Routing) notation is a compact way to specify IP addresses and their routing prefix. For example, 192.168.1.0/24 means the first 24 bits are the network part, leaving 8 bits (256 addresses) for hosts. It replaced the old Class A/B/C system.

How many hosts do I need for my subnet?

Calculate based on current devices + growth. /24 (254 hosts) is standard for small offices. /25 (126 hosts) for tiny networks. /30 (2 hosts) for point-to-point links. Always account for network and broadcast addresses—they're unusable.

What's the difference between /24 and /25?

/24 = 256 total IPs (254 usable) with subnet mask 255.255.255.0. /25 = 128 total IPs (126 usable) with subnet mask 255.255.255.128. Each increase in CIDR number cuts the network in half.

What are network and broadcast addresses?

Network address (first IP) identifies the subnet itself. Broadcast address (last IP) sends packets to all hosts in the subnet. Both are reserved and cannot be assigned to devices. Example: in 192.168.1.0/24, .0 is network, .255 is broadcast.

IPv4 vs IPv6 subnetting differences?

IPv4 uses 32-bit addresses with network/broadcast addresses. IPv6 uses 128-bit addresses with no broadcast (uses multicast instead). Standard IPv6 subnet is /64. IPv6 has so many addresses that conservation isn't a concern—focus on logical structure.

What's a subnet mask vs wildcard mask?

Subnet mask: 1s = network bits, 0s = host bits (e.g., 255.255.255.0). Wildcard mask: inverse of subnet mask, used in ACLs (e.g., 0.0.0.255). Wildcard 0 = match exactly, 1 = ignore. Convert between them by flipping all bits.

How do I calculate required CIDR from host count?

Add 2 to host count (for network/broadcast). Find next power of 2. Subtract exponent from 32. Example: need 50 hosts → 50+2=52 → next power of 2 is 64 (2^6) → 32-6 = /26 CIDR.

Can I use 192.168.x.x or 10.x.x.x for public IPs?

No! 192.168.0.0/16, 10.0.0.0/8, and 172.16.0.0/12 are private (RFC 1918) and not routable on the internet. Use them internally only. Public IPs must be assigned by your ISP or a Regional Internet Registry (RIR).