Free › CIDR Calculator
Free live tool
CIDR and subnet calculator.
IPv4 and IPv6. Ranges, masks, splits and checks, in one place.
Runs in your browser. Nothing you type is uploaded.
Calculator
Type a network. Get the answers.
Try 192.168.1.0/24, 10.1.2.3 255.255.0.0 or 2001:db8::/32.
Is an address inside?
Split into smaller subnets
Turn a range into CIDR blocks
What is CIDR
An address and a length.
The slash
How many bits are the network.
In 192.168.1.0/24, the first 24 bits name the network. The rest, 8 bits, are for hosts. A bigger number means a smaller network.
IPv4
32 bits.
A /24 holds 256 addresses, and 254 can be used for devices. The first is the network, the last is the broadcast. A /31 is for point-to-point links.
IPv6
128 bits.
The standard subnet is a /64, with 18 quintillion addresses. Home and office networks usually get a /56 or /48 to split up.
Counting the wrong hosts.The network and broadcast addresses are not usable in IPv4 (except /31 and /32), which is why a /24 gives 254, not 256.
Overlapping ranges.Two networks that overlap cause routing and firewall surprises. Use the check above before you plan an address space.
Treating IPv6 like IPv4.You do not conserve addresses in IPv6. Use a /64 for every LAN, and plan in whole prefixes.
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