IPv4 CIDR & Subnet Calculator
Inspect an IPv4 subnet without converting binary values by hand. Enter an address with CIDR notation, or provide a dotted subnet mask, and review network boundaries and address counts.
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PixelOkay · Developer toolsHow to use IPv4 CIDR & Subnet Calculator
- Enter IPv4/CIDR such as 192.168.1.42/24. Optionally enter a dotted mask to override the prefix length.
- Choose readable text or structured JSON output, then calculate the subnet.
- Review network, broadcast, first/last usable addresses and counts. Copy or download the chosen representation.
When to use this tool
Plan an IPv4 subnet or check the address range represented by a CIDR prefix. This is address arithmetic, not a network discovery or connectivity test.
CIDR and dotted masks describe the same boundary
A /24 prefix fixes the first 24 bits, equivalent to 255.255.255.0. A valid dotted mask consists of contiguous one bits followed by zero bits. Conventional subnets exclude network and broadcast addresses from the usable range. This calculator treats /31 as a point-to-point pair and /32 as a single host rather than subtracting two addresses from them.
Worked example
Input: 192.168.1.42/24
Network: 192.168.1.0/24
Mask: 255.255.255.0
Broadcast: 192.168.1.255
Usable: 192.168.1.1–192.168.1.254Limits and output checks
IPv4 only; the tool does not allocate addresses, probe hosts, inspect routing or confirm that an address is available. The word broadcast in the report describes the calculated last address; /31 point-to-point operation does not use it as a conventional broadcast endpoint.
Reference: IPv4 /31 point-to-point addressing.
Frequently asked questions
Can I use 255.255.255.0 instead of /24?
Yes. Enter it in the optional mask field. A supplied mask takes precedence over a CIDR suffix.
Why is a mask rejected?
Its octets must be valid and the binary mask must be contiguous. For example, 255.0.255.0 is not a valid contiguous subnet mask.
Are /31 and /32 ranges supported?
Yes. /31 reports two point-to-point endpoints; /32 reports one host. Validate the actual network deployment separately.
Inspect an IPv4 network without probing it
Enter an IPv4 address and CIDR prefix or a supported mask. Read the calculated range as arithmetic for that input rather than an availability report.
Scope of this workflow
The calculator does not allocate addresses, scan hosts or inspect routes. IPv4 results do not describe IPv6 behavior.
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