Subnet / CIDR Calculator
Calculate network address, broadcast, usable hosts, subnet mask and binary representation for any IPv4 CIDR block.
Calculate network address, broadcast, usable hosts, subnet mask and binary representation for any IPv4 CIDR block.
This free Subnet / CIDR Calculator from KX Toolkit is part of our all-in-one online toolkit. It runs entirely in your browser, so your data never leaves your device for client-side operations. 100% free, forever - no paywall, no credit card, no trial.
How to use the Subnet / CIDR Calculator
- Paste your input - JSON, regex pattern, JWT, URL etc.
- Pick any flags or options the tool supports.
- Click the action button (Format, Test, Decode).
- Copy the result or download it as a file.
What you can do with the Subnet / CIDR Calculator
- Format and validate API responses while debugging.
- Test regex patterns against real input before deploying.
- Decode JWTs to inspect claims and expiry.
- Generate UUIDs for migrations, tests and seeders.
Why use KX Toolkit's Subnet / CIDR Calculator
- Browser-based: Works on Windows, macOS, Linux, iOS and Android - no install, no extension.
- Privacy-first: Client-side tools never upload your data; server-side tools delete files right after processing.
- Mobile-friendly: Full feature parity on phones and tablets - not a stripped-down view.
- Fast: Optimised for instant feedback. No artificial waiting screens, no email-gated downloads.
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What is CIDR notation and what does the slash mean?
CIDR notation writes an IP plus a slash and a number, like 192.168.1.0/24. The number after the slash is the prefix length - how many leading bits identify the network, with the rest being host bits. /24 means 24 network bits and 8 host bits, giving 256 addresses. Smaller numbers mean larger networks; /16 is 65,536 addresses.
How many usable hosts does a subnet have?
For IPv4, take 2 to the power of host bits, then subtract 2 - one for the network address and one for the broadcast address, neither of which can be assigned to a host. A /24 has 256 addresses but only 254 usable. /30 has 4 addresses and 2 usable, often used for point-to-point links. /31 is a special case used in some routing setups.
What is the difference between network address and broadcast address?
The network address is the first address in the block with all host bits set to zero - it identifies the network itself and is not assigned to any device. The broadcast address has all host bits set to one and is used to send a packet to every host on the segment. Both are reserved and cannot be used as a host IP in regular IPv4 routing.
How do I split a network into smaller subnets?
Borrow bits from the host portion. A /24 split into four equal subnets becomes four /26 networks of 64 addresses each. The first /26 starts at .0, then .64, .128, .192. This is variable length subnet masking (VLSM) when subnets are different sizes; the calculator helps work out the boundaries without manual binary math.
What is a private IP range?
RFC 1918 reserves three ranges for private use: 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. These addresses are not routable on the public internet and are used inside organizations behind NAT. Pick the smallest range that fits your scale; a home network usually only needs 192.168.0.0/24, while a large enterprise will use 10.0.0.0/8 for room to grow.
Does the calculator support IPv6?
IPv6 uses the same CIDR notation but with much larger prefix lengths, typically /48 or /64 for end-user assignments. Subnetting math is similar but the numbers explode - a /64 has 18 quintillion addresses. Many calculators include an IPv6 mode; for IPv4 the math is small enough to do mentally once you know the powers of 2 up to 32.
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