If you bid for or deliver public-sector software, an ISO COSMIC functional size gives you a technology-neutral measure of what the buyer is actually asking for -- independent of your architecture, team size or delivery method. The method is the same one described on our Government functional-sizing page; this page asks the supplier's question rather than the buyer's.
BEFORE THE BID
Size the scope, then price it
A COSMIC count from the buyer's requirements or specification gives you an objective basis for effort and cost, before commercial pressure to anchor on a number. It separates "how much software is being asked for" from "how much will it cost us to build".
EVIDENCE THE ESTIMATE
Defend the number, not just assert it
A functional size plus your own calibrated productivity evidence turns an estimate into something you can walk a buyer or an assurance panel through, rather than a figure that has to be trusted on reputation alone.
AT MILESTONE REVIEW
Track scope growth explicitly
Requirements move during delivery. Re-sizing at each milestone gives you a defensible, contemporaneous record of scope change -- useful for change control, variation claims and post-delivery review alike.
FOR BUYERS / FOR SUPPLIERS
This page is the supplier-side view. Public-sector buyers sizing a programme before funding it should read the Government functional-sizing page, which sets out the method, the standards (ISO COSMIC, IFPUG) and the public-purse savings case in full.