/tools/ip-subnet-calculator
IP & Subnet Calculator
Calculate IPv4 and IPv6 CIDR ranges, subnet masks, usable hosts, cloud reservations, splits and aggregation with exact local arithmetic.
1. Calculate
Address and CIDR
2. Split
Divide a CIDR
Up to 10,000 child ranges.
3. Size
Recommend a prefix
4. Aggregate
Combine adjacent routes
IPv4 and IPv6 must be aggregated separately.
/worked examples
Common IP calculator examples
| Question | Input | What the result demonstrates | Try it |
|---|---|---|---|
| What network contains this host? | 192.168.50.42/24 | Network, broadcast, mask and usable IPv4 range | |
| How does a point-to-point subnet work? | 198.51.100.10/31 | Two usable RFC 3021 addresses without broadcast exclusion | |
| What is an IPv6 /64 range? | 2001:db8:1234:5678::1/64 | Canonical IPv6 network and exact 128-bit address count | |
| How many AWS addresses are usable? | 10.20.30.40/24 | Informational AWS primary IPv4 reservations |
The public CIDR test vectors and reproduction notes cover IPv4, IPv6 and special prefixes.
/reference
CIDR special cases
| Range | Behaviour |
|---|---|
| IPv4 /31 | Two point-to-point addresses; no network or broadcast exclusion. |
| IPv4 /32 | One host route. |
| IPv6 /127 | Two point-to-point addresses. |
| IPv6 /128 | One IPv6 address. |
/cloud profiles
Validated reservation calculations
The profiles accept documented IPv4 subnet sizes only: AWS /16–/28, Azure /2–/29 and Google Cloud primary ranges /4–/29. AWS and Azure reserve the first four and final address; Google Cloud primary ranges reserve the first two and final two. Provider-specific services, secondary ranges and bring-your-own-IP exceptions can differ, so verify the current AWS, Azure and Google Cloud documentation before deployment.
/faq
IP and subnet calculator questions
What does CIDR notation mean?
CIDR combines an IP address with a slash prefix. For example, 192.168.50.42/24 says that the first 24 bits identify the network.
Is any address sent to a lookup service?
No. The tool performs deterministic local arithmetic and does not geolocate or validate ownership.
Does this IP calculator support IPv6?
Yes. Standard IPv4 and IPv6 arithmetic uses exact BigInt values, including /127 and /128 cases. Cloud reservation profiles apply only to their supported IPv4 subnet sizes.
How are cloud-reserved addresses calculated?
The selected profile validates the address family and provider prefix range before applying its documented unusable-address offsets. Unsupported combinations return an error instead of an estimated range.
What is route aggregation?
Adjacent sibling CIDRs can be combined into their common parent when the boundary and prefix permit it. Contained child ranges are removed.