Supernet Calculator
Find a covering parent prefix.
Supernet Calculator: inputs and results
Enter an IP address, CIDR prefix, or range. Then check its first and last address below.
Calculated Boundaries & ParametersReady
Key Capabilities
- •100% Client-Side: Zero telemetry or server latency.
- •RFC Compliant: Exact 32-bit and 128-bit integer precision.
- •Quick Copy: Instant access to CIDR, mask, and range bounds.
- •Cross-Platform: Works on desktop, tablet, and mobile browsers.
Related Planning, VLSM & CloudAll Tools
VLSM Calculator
Allocate differently sized subnets.
VLSM Allocation Validator
Check alignment, capacity, and overlaps.
Exact CIDR Aggregator
Merge prefixes without adding addresses.
Route Summary Calculator
Summarize networks and identify included gaps.
DHCP Scope Calculator
Plan allocation boundaries within a subnet.
DHCP Exclusion Calculator
Remove specified addresses and ranges.
How Supernet Calculator Works?
This tool works by finding the longest prefix shared by the lowest and highest address of all input networks, which gives the smallest single parent prefix that covers every input.
Enter the networks
Type the networks to cover, such as
172.16.12.0/24to172.16.15.0/24.Find the outer bounds
The calculator takes the lowest start and the highest end of all inputs.
Count the shared bits
The common leading bits of both bounds set the supernet prefix.
Report coverage
The calculator returns the supernet and flags any addresses it covers beyond the inputs.
Supernet Calculator Formula
The formula is p = 32 − bitlength(MinStart XOR MaxEnd), and Supernet = (MinStart AND Mask(p))/p.
Differing bits
D = MinStart XOR MaxEnd1 bits mark positions that differ.
Supernet prefix
p = 32 − bitlength(D)Shared leading bits.
Extra addresses
2^(32−p) − Σ input sizesSpace covered beyond the inputs.
Exact supernet
Extra = 0Inputs fill the supernet completely.
Worked example: 172.16.12.0/24 – 172.16.15.0/24
Octet 3: 12 = 00001100, 15 = 00001111 Shared bits = 16 + 6 = 22 Supernet = 172.16.12.0/22 Extra addresses = 1,024 − 1,024 = 0 → exact
Supernet Calculator Conversion Table
The table finds the covering supernet for 7 groups of networks and shows how many extra addresses each supernet adds.
| Input Networks | Supernet | Input Size | Supernet Size | Extra |
|---|---|---|---|---|
| 172.16.12.0/24, 172.16.13.0/24, 172.16.14.0/24, 172.16.15.0/24 | 172.16.12.0/22 | 1,024 | 1,024 | 0 |
| 192.168.0.0/24, 192.168.1.0/24 | 192.168.0.0/23 | 512 | 512 | 0 |
| 192.168.1.0/24, 192.168.2.0/24 | 192.168.0.0/22 | 512 | 1,024 | 512 |
| 10.1.0.0/16, 10.2.0.0/16, 10.3.0.0/16 | 10.0.0.0/14 | 196,608 | 262,144 | 65,536 |
| 10.0.0.0/25, 10.0.0.128/26 | 10.0.0.0/24 | 192 | 256 | 64 |
| 203.0.113.0/26, 203.0.113.192/26 | 203.0.113.0/24 | 128 | 256 | 128 |
| 100.64.0.0/11, 100.96.0.0/11 | 100.64.0.0/10 | 4,194,304 | 4,194,304 | 0 |
What is Supernet Calculator?
The Supernet Calculator is a tool that finds the shortest single prefix covering a group of smaller IPv4 networks.
Supernetting is the reverse of subnetting: bits move from the network field back into the host field. 4 contiguous, aligned /24 networks combine into 1 /22. Routers advertise the supernet instead of 4 routes, which shrinks routing tables.
Non-aligned groups produce larger supernets than expected. 192.168.1.0/24 and 192.168.2.0/24 need a /22, which covers 2 extra /24 networks.
What are the uses of Supernet Calculator?
There are 4 main uses of the Supernet Calculator, including route summarization, VPC sizing, and firewall simplification.
Summarizing routes
A distribution router advertises 1 supernet for all access-layer subnets.
Sizing a VPC or VNet
The supernet of all planned subnets is the minimum network CIDR.
Simplifying firewall rules
1 supernet rule replaces several subnet rules.
Planning site blocks
Site subnets are grouped under 1 supernet for clean regional routing.