Use of a requirements sizing matrix is recommended to identify the counts of high level requirements and some of the basis for the counts.  Figure 10 illustrates a system at a point in time during the development of the testable requirements inventory.

Requirements Status
Intermediate Level Requirements
Testable Requirements
HLR
Number To-date
%
Identified
Projected Total
Estimated TRs per ILR
Projected Total
Accounting
32
80%
40
48
1920
Administration
57
80%
71
20
1425
Audit and Control
9
100%
9
2
18
Communication
28
85%
33
7
231
Conversion
27
50%
54
20
1080
Bank Interface
28
85%
33
15
494
Network Interface
4
50%
8
10
80
Credit Card Interface
23
75%
31
20
613
Operations
25
85%
29
18
529
Order Maintenance
79
95%
83
20
1663
Pilot Installation
9
30%
30
33
990
Reporting
67
75%
89
20
1787
Services
43
92%
47
40
1870
Usability
40
41%
97
6
585
Performance
0
0%
0
0
0
Totals
471
72%
654
13285

Requirements Sizing Matrix
Figure 10

The matrix lists the HLRs identified and for each HLR, the number of ILRs identified to-date.  The next column shows the percent of ILRs identified to-date.  This percentage can then be used to project the total estimated ILRs for each HLR.  The right side of the matrix contains the estimated TRs.  An estimated number of TRs per ILR can be documented and used to project the total TRs for each HLR.  These can be totaled to achieve the total size measurement.  

Any HLR in the matrix with a size of zero indicates an area of the system for which estimates cannot be completed.  This should be a red flag to project management that this area may not be sufficiently defined.