IP Address & CIDR Calculator
CIDR and subnet math stay in your browser.
Calculate IPv4 networks from CIDR or a subnet mask, split a block into equal subnets, and normalize IPv6 prefixes — locally, with no upload.
Enter an IPv4 address with a CIDR prefix, or switch to IP + subnet mask, to calculate network, broadcast, and usable hosts.
Addresses and prefixes entered here are processed locally in your browser and are not sent to a server. This page does not look up public or geolocation data.
Online IP Calculator, CIDR Calculator & Subnet Calculator
Looking for an online IP calculator, CIDR calculator, subnet calculator, or IPv4 / IPv6 calculator? Toolshelf turns 192.168.1.0/24 — or an address plus a subnet mask — into network, broadcast, wildcard, host range, and usable counts in your browser. Nothing is uploaded.
Need binary, hex, or IPv4-mapped forms instead of subnet math? Use the IP Address Converter. This page is the calculator: CIDR, masks, equal subnet splits, and IPv6 prefix parsing.
What you can calculate
- Calculate IPv4 networks from CIDR such as 192.168.1.0/24
- Calculate the same result from an IP address plus a subnet mask
- Show network, broadcast, wildcard, and usable host range
- Count total addresses and usable hosts, including /31 and /32
- Split a parent network into equal subnet ranges
- Validate IPv4, IPv6, and CIDR independently
- Compress, expand, and parse IPv6 prefixes
- Copy one field or the full result set
- Private by design: all math runs in your browser
CIDR vs subnet mask vs wildcard
CIDR writes the prefix as a slash length. Subnet mask writes the same bits in dotted decimal. A wildcard is the inverted mask. All three describe one block.
| CIDR | Subnet mask | Usable hosts |
|---|---|---|
| /24 | 255.255.255.0 | 254 |
| /25 | 255.255.255.128 | 126 |
| /30 | 255.255.255.252 | 2 |
| /31 | 255.255.255.254 | 2 (RFC 3021) |
How subnet splitting works
Equal subnets borrow host bits from the parent prefix. Four subnets need two bits, so a /16 becomes four /18 networks. If you ask for three, the calculator still creates four — the next power of two — because CIDR blocks are binary sizes. It will not invent unequal VLSM slices or overlapping ranges.
A host address is aligned to the parent network first. 192.168.10.20/16 is treated as 192.168.0.0/16 before the split.
Classful labels vs CIDR
The table still shows a historical class (A, B, C, D, or E) from the first octet when that is meaningful. Routing today uses CIDR, not classful defaults. A 192.x address is Class C historically, even when you subnet it as /20. Multicast (D) and reserved (E) ranges are labeled so they are not treated as ordinary host subnets.
IPv6 calculations this tool will and will not do
IPv6 has no broadcast address and a 128-bit space, so enumerating millions of child prefixes is not useful. This calculator validates addresses, compresses and expands them (RFC 5952 style), and parses CIDR to show the network prefix, range start/end, and address count. It does not claim a public IPv6 lookup or a conversion of IPv4 into native globally routable IPv6.
Common use cases
Firewall and security-group rules
Confirm the exact network, broadcast, and usable range before you paste a CIDR into a cloud ACL or on-prem firewall.
VPC and VLAN planning
Split a /16 or /8 into equal subnets and copy the resulting CIDR blocks into Terraform, Ansible, or a spreadsheet.
VPN and DHCP scopes
See first and last usable addresses when you size a pool so the gateway and broadcast stay outside the lease range.
Log and packet review
Check whether a source IP sits inside a documented prefix, and compare wildcard masks used by some Cisco-style ACLs.
IPv6 prefix checks
Expand compressed addresses and parse /32, /48, or /64 documentation prefixes when reviewing AAAA records or dual-stack configs.
Teaching CIDR math
Show classful history next to modern CIDR so students can see why /24 is common without treating classful masks as current practice.
How to use the IP & CIDR calculator
- 1Choose IPv4 / CIDR, Subnet, IPv6, or Validate.
- 2Enter CIDR, an IP plus mask, a parent network and subnet count, or an IPv6 address.
- 3Read the result table as you type. Invalid input shows a clear error instead of a guessed network.
- 4Use Copy on a row, Copy all, or Reset the current tab.
Privacy-first network math
Internal ranges, customer prefixes, and VPN pools should not be posted to a remote lookup service. Toolshelf computes CIDR and subnet values locally. After the page loads, calculation does not need another network request.
For cookies, logs, and advertising partners, read our Privacy Policy.
Limitations
- This is not a public-IP or geolocation lookup.
- Subnet split creates equal power-of-two blocks, not arbitrary VLSM trees.
- Very large splits show the first 256 rows so the page stays usable.
- IPv6 has no broadcast; usable-host conventions from IPv4 do not apply.
Frequently asked questions
What is an IP calculator?
An IP calculator turns an address and prefix into network details: subnet mask, wildcard, network address, broadcast, host range, and address counts. This Toolshelf page does that for IPv4 CIDR and subnet masks, and it also validates and normalizes IPv6.
What is a CIDR calculator?
A CIDR calculator reads notation such as 192.168.1.0/24 and derives the block size from the prefix length. /24 means the first 24 bits are the network; the remaining 8 bits are hosts (256 addresses, 254 typically usable).
How do I use a subnet calculator?
Enter a parent network (for example 192.168.0.0/16) and the number of equal subnets you need. The tool borrows the fewest bits that can hold that count, then lists each child network, broadcast, and host range.
Can I calculate from a subnet mask instead of CIDR?
Yes. Choose IP + subnet mask and enter values such as 192.168.1.0 and 255.255.255.0. The mask must be contiguous ones followed by zeros; 255.255.0.255 is rejected.
What is a wildcard mask?
A wildcard mask is the inverse of the subnet mask. For 255.255.255.0 the wildcard is 0.0.0.255. Some ACL syntax uses wildcards instead of prefix lengths.
How many usable hosts are in a /24?
A /24 has 256 addresses. Conventionally the first is the network and the last is broadcast, leaving 254 usable hosts. /31 follows RFC 3021 (both addresses usable on point-to-point links). /32 is a single host route.
Does this IPv6 calculator invent a native IPv6 address from IPv4?
No. It validates, compresses, expands, and parses IPv6 CIDR. An IPv4-mapped form such as ::ffff:192.168.1.1 is a representation, not a globally routable IPv6 equivalent of that IPv4 address.
Is this IP subnet calculator private?
Yes. Calculation runs in your browser. Addresses are not uploaded and are not written into the page URL.
Do I need an account to use the IP calculator?
No. Toolshelf IP Address & CIDR Calculator requires no account. Addresses you enter are not processed on a server.
Does the calculator work on mobile?
Yes. Controls stack on small screens. Wide subnet tables scroll inside the tool pane so the rest of the page does not overflow horizontally.
Related guides
Short articles that explain the problem this tool solves.
- What Is CIDR? — CIDR writes an IP prefix and length, such as 10.0.0.0/24. Learn how slash notation maps to masks, host counts, and why /24 is not the same as a single address.
- IPv4 vs IPv6: What Developers Should Know — A practical overview of IPv4 and IPv6 addressing, CIDR basics, and when an IP converter helps during network debugging.
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Ready to calculate a CIDR block?
Scroll up, enter a prefix or mask, and copy the table.
Back to calculatorWhat would you like to do next?
Continue working with the next step in this workflow. Recently used tools in this set are listed first.
- IP Address Converter & Analyzer — Online IP address converter and analyzer.
- User-Agent Parser & Analyzer — Online User-Agent Parser and Analyzer.
- Regex Tester — Online Regex Tester and Debugger.
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Related guides
Short articles that explain the problem this tool solves.
- What Is CIDR? — CIDR writes an IP prefix and length, such as 10.0.0.0/24. Learn how slash notation maps to masks, host counts, and why /24 is not the same as a single address.
- IPv4 vs IPv6: What Developers Should Know — A practical overview of IPv4 and IPv6 addressing, CIDR basics, and when an IP converter helps during network debugging.
You may also need
Continue with related browser-based tools on Toolshelf.
- IP Address Converter & Analyzer — Online IP address converter and analyzer.
- User-Agent Parser & Analyzer — Online User-Agent Parser and Analyzer.
- Regex Tester — Online Regex Tester and Debugger.
- Cron Expression Generator — Online cron expression generator and explainer.
- JWT Decoder & Inspector — Online JWT decoder and inspector.
- Chmod Calculator — Chmod calculator online.
- Docker Run to Compose — Docker run to Compose converter.
- HTTP Status Codes — HTTP status codes lookup online, plus MIME types and a Basic Auth header builder.