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Calculate CIDR Network Details
Calculate cidr from your inputs with a quick browser-based result.
Direct Answer
Use the CIDR Calculator when you need to understand an IP range, subnet mask, host count, network address, or broadcast address from CIDR notation.
Starting From a CIDR Notation String
This calculator is built around the case where you already have a CIDR string, like 192.168.1.0/24 or 10.20.30.0/22, from a firewall rule, cloud VPC setting, or documentation, and need to break it down into concrete numbers.
- The prefix length after the slash tells you how many bits are fixed as the network portion.
- The remaining bits are host bits, and 2 raised to that many bits gives the total address count in the block.
- Subtracting the network and broadcast addresses from the total gives the usable host count for most prefix lengths.
- The subnet mask (like 255.255.255.0) and the CIDR prefix (like /24) are two ways of writing the exact same boundary.
Edge Cases That Trip People Up
A few CIDR sizes and address ranges behave differently from the general pattern, and missing them is a common source of confusion when reading someone else's network diagram.
- A /31 has no usable network or broadcast address under RFC 3021; both addresses in the pair are usable, which is why point-to-point links commonly use /31.
- A /32 is a single host route with no network or broadcast concept at all, since there are no host bits left.
- 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16 are the private ranges reserved by RFC 1918 and never routed on the public internet.
- 127.0.0.0/8 is reserved for loopback traffic, and 169.254.0.0/16 is used for link-local addresses when DHCP fails.
How to Use CIDR Calculator
- Fill in the input fields with your values.
- The result calculates automatically as you type.
- For spreadsheet work, switch to Bulk paste and paste rows copied from Excel or Google Sheets.
- Copy the result column and paste it back into your spreadsheet.
- Use the Copy result button to copy the output to your clipboard.
- Press Reset to clear all fields and start again.
Formula Reference
| Feature | Details |
|---|---|
| Purpose | Calculate a numeric answer from the values entered. |
| Single input | Numbers, dates, rates, or options depending on the calculator. |
| Bulk input | Rows copied from Excel, Google Sheets, CSV, or tab-separated columns. |
| Bulk output | A copyable result column or full table that can be pasted back into a spreadsheet. |
| Best for | Quick checks, homework, finance estimates, planning, everyday math, and spreadsheet cleanup. |
| Category | Developer Tools |
| Works on | Desktop, tablet, and mobile browsers |
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Frequently Asked Questions
What does /24 mean in an IP address?
It means the first 24 bits of the 32-bit address are fixed as the network portion, leaving 8 bits for host addresses. That corresponds to a subnet mask of 255.255.255.0 and 256 total addresses in the block.
How do I find the network and broadcast address from CIDR notation?
Convert the address and the prefix length into a subnet mask, then AND the address with the mask to get the network address. OR the network address with the inverted mask (the wildcard mask) to get the broadcast address, which is the highest address in the range.
How many usable hosts does a /24 give?
A /24 has 256 total addresses, and subtracting the network address and broadcast address leaves 254 usable host addresses. This is one of the most common block sizes for small office or department networks.
What's different between the CIDR Calculator and the Subnet Calculator?
This tool is built for when you already have a CIDR string like 192.168.1.0/24 and want its range, mask, and host count broken down. The Subnet Calculator is more often used the other way around, when you start from a required number of hosts or subnets and need to work out what prefix length and mask satisfy that requirement, which is closer to VLSM planning.
What is a /31 subnet and why does it have no broadcast address?
A /31 leaves only 1 host bit, so under the classic rules it would have zero usable addresses since both would be network and broadcast. RFC 3021 makes an exception for point-to-point links: both addresses in a /31 pair are treated as usable host addresses, with no network or broadcast address reserved.
What is a /32 and when is it used?
A /32 has zero host bits, meaning the entire 32-bit address is fixed, so it identifies exactly one address with no concept of a network or broadcast address. It's commonly used for host routes, loopback interfaces, and firewall rules targeting a single IP.
How many usable hosts do /28 and /30 give?
A /28 has 16 total addresses minus network and broadcast, giving 14 usable hosts. A /30 has 4 total addresses minus network and broadcast, giving 2 usable hosts, which is a common size for point-to-point router links.
What are the private IP ranges?
RFC 1918 reserves 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16 for private networks; none of these are routed on the public internet. Devices inside these ranges typically reach the internet through NAT at a router or gateway.
What is 127.0.0.0/8 used for?
The entire 127.0.0.0/8 block is reserved for loopback traffic, meaning any address in that range refers back to the local machine itself. 127.0.0.1 is the most commonly used address in that block.
What is 169.254.0.0/16 used for?
This is the link-local (APIPA) range that a device automatically assigns itself when it can't reach a DHCP server. Seeing a 169.254.x.x address usually means DHCP failed, not that the device intentionally chose that address.
How does CIDR notation relate to a subnet mask like 255.255.255.0?
They describe the exact same boundary in two different formats. /24 and 255.255.255.0 both mean 24 network bits and 8 host bits; converting between the two is just a matter of counting or expanding consecutive 1 bits.
What is a wildcard mask and how is it different from a subnet mask?
A wildcard mask is the bitwise inverse of a subnet mask, most commonly seen in Cisco ACL configurations. Where a subnet mask has a 1 for network bits and a 0 for host bits, the wildcard mask flips that, using 0 for the fixed portion and 1 for the portion allowed to vary.
How do I check if two CIDR ranges overlap?
Compare the network address and broadcast address of each range; if either range's boundaries fall inside the other's range, they overlap. This matters when allocating VPC subnets or firewall rules to avoid routing conflicts.