Subnet Calculator

Calculate IPv4 and IPv6 subnets instantly — network and broadcast address, usable host range, mask and CIDR — or split a network into smaller subnets. Everything runs in your browser; nothing is uploaded.

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100% free, no sign-up Runs in your browser — nothing uploaded Instant, works offline
What is a subnet? CIDR notation explained CIDR notation chart IPv4 vs IPv6 subnetting VLSM & subnet splitting

How Does the Subnet Calculator Work?

Three steps, all in your browser.

1

Enter an address and prefix

Type a CIDR block such as 192.168.1.0/24 or 2001:db8::/48 — or an IPv4 address with a dotted mask like 10.0.0.0 255.0.0.0. The tool detects IPv4 vs IPv6 automatically. New to this? Read what a subnet is.

2

Read the full breakdown

Get the network and broadcast address, usable host range, total and usable host counts, subnet mask, wildcard mask, CIDR and binary mask — computed with exact 32-bit and 128-bit math. Press Enter to calculate without leaving the keyboard.

3

Split into subnets

Switch to Split into subnets to carve a block into equal pieces — by number of subnets or by hosts per subnet — and get a table of every resulting subnet. That is the core of VLSM subnetting.

Frequently Asked Questions

What does a subnet calculator do?
A subnet calculator turns an IP address and a prefix length — written in CIDR form like 192.168.1.0/24 — into every value you need to plan or document a network. From that single input it derives the network (base) address, the broadcast address, the first and last usable host, the total and usable host counts, the subnet mask, the wildcard mask, and the binary form of the mask. It works for both IPv4 and IPv6, detecting the version automatically. The tool runs entirely in your browser using exact 32-bit (IPv4) and 128-bit (IPv6) arithmetic, so there is no rounding error and nothing is sent to a server. It saves you from doing bitwise AND/OR math by hand and from the off-by-one mistakes that are easy to make with broadcast addresses and usable ranges.
Is my IP data sent to a server?
No. The subnet calculator runs entirely in your browser with JavaScript — all of the bitwise math happens locally on your device. Nothing you type is uploaded, logged, or stored anywhere, and once the page has loaded you can use it offline with no network connection at all. That makes it safe for internal addressing plans, customer networks, and other information you would not want to paste into a third-party website. There is no account, no login, and no tracking of the addresses you calculate. If you want to confirm this, open your browser's network tab while you use the tool: you will see no outbound requests when you press Calculate.
What is CIDR notation and how do I read it?
CIDR (Classless Inter-Domain Routing) notation writes a network as an address followed by a slash and a prefix length, for example 192.168.1.0/24 or 2001:db8::/48. The number after the slash is how many leading bits are fixed as the network portion; the remaining bits identify hosts within that network. A larger prefix means a smaller network: a /24 has 8 host bits (256 addresses), while a /26 has 6 host bits (64 addresses). For IPv4 the prefix runs from 0 to 32; for IPv6 it runs from 0 to 128. CIDR replaced the old class A/B/C system, letting networks be sized to need. See CIDR notation explained for a full walkthrough.
How many usable hosts are in a subnet?
For IPv4, the total number of addresses is 2 raised to the number of host bits (32 minus the prefix). Two addresses are normally reserved — the network address and the broadcast address — so the usable host count is 2^(32 − prefix) − 2. A /24 has 256 total and 254 usable; a /26 has 64 total and 62 usable; a /30 has 4 total and 2 usable. Two special cases exist: a /31 gives 2 usable addresses for point-to-point links (RFC 3021, no broadcast), and a /32 describes a single host. IPv6 does not reserve a broadcast address and subnets are astronomically large, so the calculator reports IPv6 capacity as a power of two (a /64 holds 2^64 addresses) rather than subtracting two.
What is the difference between IPv4 and IPv6 subnetting?
The principle is the same — a prefix length splits the address into a network part and a host part — but the scale and conventions differ. IPv4 addresses are 32 bits, written as four decimal octets, and subnets are small enough that you carefully count usable hosts and reserve a broadcast address. IPv6 addresses are 128 bits, written as eight groups of hexadecimal, and there is no broadcast address, so no addresses are subtracted. The de-facto standard subnet size in IPv6 is /64, which already contains 2^64 addresses, so IPv6 subnetting is usually about how you allocate /48s and /56s to sites rather than conserving host addresses. See IPv4 vs IPv6 subnetting for the details.
How do I split a network into smaller subnets?
Switch the calculator to Split into subnets mode and enter your base block (for example 192.168.1.0/24). You can split either by the number of equal subnets you need or by the number of hosts each subnet must hold. The tool picks the smallest prefix that satisfies your requirement, then lists every resulting subnet with its network address, usable host range, broadcast address and host count. Splitting by 4 subnets turns a /24 into four /26 blocks; splitting a /24 to fit 50 hosts per subnet also yields /26 blocks. This is the everyday building block of VLSM (Variable Length Subnet Masking), where one range is carved into right-sized pieces instead of wasting a fixed block on each segment.