/tools/ip-subnet-calculator
IP Subnet Calculator
Calculate IPv4 and IPv6 CIDR ranges, special cases, cloud reservations, splits and aggregation with exact BigInt arithmetic.
1. Calculate
Address and CIDR
Enter an address and prefix.
2. Split
Divide a CIDR
Up to 10,000 child ranges.
3. Size
Recommend a prefix
Reservation profile is shared with the calculator.
4. Aggregate
Combine adjacent routes
IPv4 and IPv6 must be aggregated separately.
Ready. All address arithmetic stays in this browser.
/reference
CIDR special cases
| Range | Behaviour |
|---|---|
| IPv4 /31 | Two point-to-point addresses; no network/broadcast exclusion. |
| IPv4 /32 | One host route. |
| IPv6 /127 | Two point-to-point addresses. |
| IPv6 /128 | One IPv6 address. |
/cloud profiles
Informational reservation calculations
AWS and Azure reserve the first four and final IPv4 address; Google Cloud primary IPv4 ranges reserve the first two and final two. Verify current platform behaviour in the official AWS, Azure and Google Cloud documentation.
/faq
Subnet questions
Is any address sent to a lookup service?
No. The tool performs deterministic local arithmetic and does not geolocate or validate ownership.
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.