Subnet Calculator
Calculate IPv4 subnet details from an IP address and CIDR prefix. Get network/broadcast addresses, host range, wildcard mask, binary breakdown, and split subnets visually.
Subnet Calculator
Calculate network details from an IP address and subnet mask or CIDR notation.
| Field | Octet 1 | Octet 2 | Octet 3 | Octet 4 | Decimal |
|---|---|---|---|---|---|
| IP Address | 11000000 | 10101000 | 00000001 | 00000000 | 192.168.1.0 |
| Subnet Mask | 11111111 | 11111111 | 11111111 | 00000000 | 255.255.255.0 |
| Network | 11000000 | 10101000 | 00000001 | 00000000 | 192.168.1.0 |
| Broadcast | 11000000 | 10101000 | 00000001 | 11111111 | 192.168.1.255 |
Subnet Splitter
Split 192.168.1.0/24 into smaller subnets:
| # | Network | Range | Broadcast | Hosts |
|---|---|---|---|---|
| 1 | 192.168.1.0/25 | 192.168.1.1 - 192.168.1.126 | 192.168.1.127 | 126 |
| 2 | 192.168.1.128/25 | 192.168.1.129 - 192.168.1.254 | 192.168.1.255 | 126 |
Common Private Ranges
What is a Subnet Calculator?
A subnet calculator takes an IPv4 address and a subnet mask (or CIDR prefix length) and computes the full network details: network address, broadcast address, usable host range, wildcard mask, and more. It is essential for network engineers, sysadmins, and anyone studying for Cisco CCNA, CompTIA Network+, or similar certifications.
Key Features
- Full Subnet Details: Network address, broadcast, first/last host, total addresses, usable hosts, IP class, and type (private/public/loopback).
- Binary Breakdown: See every address in binary, octet by octet, with a visual mask showing network vs host bits.
- Subnet Splitter: Divide a network into smaller subnets by choosing a longer prefix. See all resulting subnets with their ranges.
- CIDR Support: Enter addresses in CIDR notation (e.g. 192.168.1.0/24) or select the prefix from a dropdown.
- Common Presets: One-click presets for RFC 1918 private ranges, loopback, and link-local networks.
- IPv6 Mapped: Shows the IPv4-mapped IPv6 address and hex notation.
How to use the Subnet Calculator
- Enter an IPv4 address (e.g. 192.168.1.0) or paste a CIDR block (e.g. 10.0.0.0/16).
- Select the subnet prefix length from the dropdown or quick-select buttons.
- Click Calculate to see all network details, binary breakdown, and mask visualization.
- Use the Subnet Splitter to divide the network into smaller subnets.
Understanding CIDR Notation
CIDR (Classless Inter-Domain Routing) notation appends a prefix length to an IP address, like 192.168.1.0/24. The prefix length indicates how many leading bits of the address identify the network. A /24 means 24 network bits and 8 host bits, giving 256 total addresses (254 usable hosts).
Subnet Mask Cheat Sheet (/8 to /32)
The table every network engineer keeps taped to a monitor. Usable hosts is total addresses minus the network and broadcast address.
| CIDR | Subnet mask | Usable hosts | Typical use |
|---|---|---|---|
| /8 | 255.0.0.0 | 16,777,214 | Class A, 10.0.0.0/8 private range |
| /16 | 255.255.0.0 | 65,534 | Class B, 172.16.0.0/16, large sites |
| /22 | 255.255.252.0 | 1,022 | Campus or large office network |
| /23 | 255.255.254.0 | 510 | Two merged /24 networks |
| /24 | 255.255.255.0 | 254 | The standard LAN, 192.168.1.0/24 |
| /25 | 255.255.255.128 | 126 | Half a /24 |
| /26 | 255.255.255.192 | 62 | Quarter of a /24, small VLANs |
| /27 | 255.255.255.224 | 30 | Small office or device VLAN |
| /28 | 255.255.255.240 | 14 | Small cloud subnets, DMZ segments |
| /29 | 255.255.255.248 | 6 | ISP customer block, firewall segment |
| /30 | 255.255.255.252 | 2 | Router-to-router links |
| /31 | 255.255.255.254 | 2 | Point-to-point links (RFC 3021, no broadcast) |
| /32 | 255.255.255.255 | 1 | Single host route, loopbacks |
An online alternative to ipcalc
If you use ipcalc on Linux, this calculator covers the same job in the browser: the binary breakdown with network and host bits highlighted, wildcard masks for Cisco ACLs, and the subnet splitter for dividing a block into smaller networks. Everything runs client-side, so no addresses ever leave your machine, which matters when you are working with internal network plans.
Frequently Asked Questions
What is a subnet mask?
A subnet mask is a 32-bit number that splits an IP address into a network part and a host part. Bits set to 1 mark the network portion, bits set to 0 mark the host portion. For example, 255.255.255.0 (a /24) means the first 24 bits identify the network and the remaining 8 bits identify hosts, allowing 254 usable host addresses.
What does /24 mean in an IP address?
The /24 is a CIDR prefix length: the first 24 bits of the address are the network part. A /24 network like 192.168.1.0/24 has a subnet mask of 255.255.255.0, contains 256 total addresses, and offers 254 usable hosts (the first address is the network, the last is the broadcast). It is the most common size for home and office LANs.
How many hosts are in a /29 subnet?
A /29 subnet (mask 255.255.255.248) contains 8 total addresses, of which 6 are usable hosts, since one address is the network and one is the broadcast. ISPs commonly assign /29 blocks to business customers who need a handful of public IPs.
What is the difference between CIDR notation and a subnet mask?
They express the same information in two formats. CIDR notation is the compact form (/26), while the subnet mask is the dotted-decimal form (255.255.255.192). The CIDR number simply counts the 1-bits in the mask. This calculator converts between the two automatically.
Is this subnet calculator private? My network plans are sensitive.
Yes. All calculations run entirely in your browser with client-side JavaScript. No IP addresses, ranges or network plans are sent to any server, stored or logged, which makes it safe to use with internal addressing schemes.
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