CIDR Coverage Gap Calculator
Identify uncovered addresses between allocations.
CIDR Coverage Gap 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.
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How CIDR Coverage Gap Calculator Works?
This tool works by sorting the allocated blocks inside a parent prefix, walking from the parent start to the parent end, and recording every stretch of addresses no block covers.
Enter the parent prefix
Type the block to inspect, such as
10.50.0.0/22.Enter the allocations
Paste the allocated CIDR blocks, one per line.
Walk the address space
The calculator sorts the allocations and compares each block start with the end of the previous block.
List the gaps
Each gap appears as a range and as the minimal CIDR blocks that fill it.
CIDR Coverage Gap Calculator Formula
The formula is Gaps = Parent − (Allocation₁ ∪ Allocation₂ ∪ … ∪ Allocationₙ).
Gap between blocks
Gap = [End_i + 1, Start_(i+1) − 1]Exists when Start_(i+1) > End_i + 1.
Leading gap
[Parent start, Start_1 − 1]Exists when the first block starts after the parent start.
Trailing gap
[End_n + 1, Parent end]Exists when the last block ends before the parent end.
Coverage
Covered ÷ 2^(32 − p) × 100 %Share of the parent covered by allocations.
Worked example: 10.50.0.0/22 with 4 allocations
Allocations: 10.50.0.0/25, 10.50.0.192/26, 10.50.1.0/24, 10.50.3.0/27 Gap 1: 10.50.0.128 – 10.50.0.191 → 10.50.0.128/26 Gap 2: 10.50.2.0 – 10.50.2.255 → 10.50.2.0/24 Gap 3: 10.50.3.32 – 10.50.3.255 → /27 + /26 + /25 Coverage = 480 ÷ 1,024 = 46.9 %
CIDR Coverage Gap Calculator Conversion Table
The table lists the uncovered gaps inside 10.50.0.0/22 for the 4 allocations in the worked example.
| Gap Range | Addresses | CIDR Blocks |
|---|---|---|
| 10.50.0.128 – 10.50.0.191 | 64 | 10.50.0.128/26 |
| 10.50.2.0 – 10.50.2.255 | 256 | 10.50.2.0/24 |
| 10.50.3.32 – 10.50.3.255 | 224 | 10.50.3.32/27, 10.50.3.64/26, 10.50.3.128/25 |
What is CIDR Coverage Gap Calculator?
The CIDR Coverage Gap Calculator is a tool that finds the addresses inside a parent prefix that no listed allocation covers.
Address plans drift over time. Subnets are released, resized, and moved, which leaves holes. The CIDR Coverage Gap Calculator compares the allocation list with the parent block and lists every hole as a range and as CIDR blocks.
The output answers 2 questions at once: where free space exists and how large each free piece is. A gap expressed as 10.50.2.0/24 is ready to allocate as-is.
What are the uses of CIDR Coverage Gap Calculator?
There are 4 main uses of the CIDR Coverage Gap Calculator, including free-space discovery, audit checks, and route coverage.
Finding free address space
The gap list shows every unallocated block inside a site or region prefix.
Auditing IPAM data
Unexpected gaps point to missing records or released subnets that were never documented.
Checking route coverage
A summary route that includes gaps attracts traffic to addresses with no destination.
Planning consolidation
Gap sizes show whether scattered free space can host a new /24 or only smaller blocks.