| Software Size Estimation Techniques
You don't have to do a full functional size count to estimate the functional size of a development or enhancement project. There are a large number of software size estimation techniques available within the recognised sizing ranges levels 4 to 6. Three practical and well documented techniques are:
These are derived size estimation methods that use algorithms. These techniques are described in detail in chapter 5 of the book: Practical Project Estimation 2nd Edition.
The Rule of the "Thirties"
Various organisations have come up with a rule of thumb of one logical file equaling "thirty something" unadjusted function points of total software size for a development project. You can use this to obtain a rough size estimate. Their range is between 31 to 35 function points per logical file. So a system with 40 logical files can be very roughly sized as follows: 40 x 35 = 1,400 function points. This sort of rough estimate should have an allowance of + or - 30%.
How big is "big"?
Software systems vary greatly in size. Grant Rule of SMS has come up with an interesting size description concept based on the accepted sizing for clothes: XXS, XS etc. Download his paper.
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