Calculator Input
Example Data Table
| Input CIDR | Network | Mask | Usable range | Usable hosts |
|---|---|---|---|---|
| 192.168.10.25/24 | 192.168.10.0 | 255.255.255.0 | 192.168.10.1 - 192.168.10.254 | 254 |
| 10.20.5.8/30 | 10.20.5.8 | 255.255.255.252 | 10.20.5.9 - 10.20.5.10 | 2 |
| 172.16.4.100/26 | 172.16.4.64 | 255.255.255.192 | 172.16.4.65 - 172.16.4.126 | 62 |
Formula Used
Host bits: 32 - prefix
Total addresses: 2^(32 - prefix)
Traditional usable hosts: 2^(32 - prefix) - 2
Subnet mask: leading prefix bits are 1, remaining bits are 0.
Wildcard mask: 255.255.255.255 - subnet mask
Network address: address rounded down to the nearest block boundary.
Broadcast address: network address + total addresses - 1
Child subnet count: 2^(split prefix - parent prefix)
How to Use This Calculator
- Enter a full CIDR block, such as
192.168.1.44/24. - Or enter an IPv4 address and prefix in separate fields.
- Add a split prefix when you need smaller child subnets.
- Add required hosts to get a suggested prefix.
- Press calculate to show results above the form.
- Review the chart, binary values, and split table.
- Use CSV or PDF export for documentation.
CIDR Planning Guide
Why CIDR Planning Matters
Subnet planning keeps networks clear, scalable, and easier to protect. CIDR notation gives one compact way to describe an address block. It combines an IPv4 address with a prefix length. The prefix tells how many leading bits identify the network. The remaining bits define host space. Good planning prevents wasted addresses. It also helps teams avoid overlaps between offices, clouds, labs, and virtual networks.
What This Calculator Shows
This tool converts a CIDR block into practical network details. It reports the network address, broadcast address, subnet mask, wildcard mask, first usable address, last usable address, total addresses, and usable hosts. It also shows binary views. These views are helpful when learning how masks divide an address. You can enter a complete block, such as 192.168.10.25/24. You can also enter an address and prefix separately.
Advanced Subnet Splitting
The splitter helps when one large block must become smaller blocks. Enter a longer split prefix. The page lists child networks in order. Each child network includes its own usable range and capacity. This is useful for VLANs, departments, customer segments, and cloud subnets. A host requirement field can suggest the smallest safe prefix. That estimate uses traditional IPv4 host rules, so network and broadcast addresses are reserved for most subnets.
Practical Use Cases
Administrators can use this page while designing routing tables. Security teams can check firewall rules. Students can verify manual subnetting work. Developers can document private ranges before deploying services. The CSV export supports spreadsheets and audits. The PDF export gives a quick report for tickets or design notes.
Accuracy Notes
The calculator handles IPv4 math with unsigned address values. It treats /31 and /32 blocks as special small networks. A /31 is often used for point-to-point links. A /32 identifies one host route. For ordinary LAN planning, prefixes from /30 through /16 are common. Always confirm device and provider rules before applying a design.
Maintenance Benefits
Clear subnet records reduce troubleshooting time. They show which ranges belong to routers, servers, printers, guests, and management tools. When teams expand, documented blocks make change reviews faster. They also reduce accidental duplicate assignments during urgent network work today.
FAQs
1. What is CIDR notation?
CIDR notation combines an IPv4 address with a slash prefix. The prefix shows how many bits belong to the network part. For example, /24 means 24 network bits and 8 host bits.
2. What does a subnet mask do?
A subnet mask separates the network section from the host section. Binary ones mark network bits. Binary zeros mark host bits. The mask helps devices decide whether traffic is local or routed.
3. Why are two addresses often reserved?
Most traditional IPv4 subnets reserve the first address as the network address and the last address as the broadcast address. That is why usable hosts usually equal total addresses minus two.
4. What is a wildcard mask?
A wildcard mask is the inverse of the subnet mask. It is often used in routing rules, access lists, and network matching. A zero bit must match. A one bit can vary.
5. Can I split one network into smaller subnets?
Yes. Enter a split prefix that is longer than the parent prefix. The calculator lists child CIDR blocks with network, usable range, broadcast address, and host capacity.
6. What does /32 mean?
A /32 block contains one IPv4 address. It is commonly used for host routes, loopback interfaces, firewall rules, and exact address matching. It has no larger host range.
7. What does /31 mean?
A /31 block contains two addresses. It is often used on point-to-point links where broadcast is not needed. Some older equipment may still expect traditional subnet behavior.
8. Are private and public ranges detected?
Yes. The calculator labels common private, loopback, link-local, carrier-grade NAT, documentation, multicast, reserved, and public unicast ranges. This helps with planning and review.