Size and effort is all what matters eventually :-). Estimation of work is really a tricky job. Here are a few resources I think a good start point to gather estimation techniques:
Books and papers
o Brooks, F., The Mythical Man Month, Addison-Wesley
o COCOMO II Model Definition Manual, University of Southern California, 1991 (for more information visit \\.sunset.usc.edu/cse/)
o Institute of Electrical and Electronic Engineers Inc., Glossary of Software Engineering Terminology, IEEE Std 610.12-1990, The Institute of Electrical and Electronic Engineers Inc.
o International Function Point Users Group: Function Point Counting Practices Manual, Release 4.1, Jan 1999
o Jones, C., A Short History of Function Points and Feature Points, Software Productivity Research Inc., Mimeo Version, 2.0, Feb 20, 1988
o Jones, C., Applied Software Measurement - Assuring Productivity and Quality, McGraw-Hill Publishing Company, 1991
o Jones, C., What are function points, Software Productivity Research Inc. (for more information visit \\.spr.com)
o MK II Function Point Analysis Counting Practices Manual, Version 1.3.1, United Kingdom Software Metrics Association, September 1998
o Pressman, R.S., Software Engineering – A Practitioner’s Approach, Fifth Edition, McGraw-Hill Publishing Company, 2001
Web sites
o A list of resources for software process metrics, including function points, is available at \\.rspa.com/spi/metrics-process.html.
o A resource for software engineering is the Software Engineering Institute, Carnegie Mellon University, \\.sei.cmu.edu.
o A variety of lists with software engineering resources is available at \\.rspa.com/spi.
o Information on COCOMO and COCOMO II is available at \\.sunset.usc.edu/cse/.
o Information on function points is available at \\.ifpug.org.
o The information on international standards and guidelines related to software from IEEE is available at \\.ieee.org.
o The guide to the Software Body of Knowledge is available at \\.swebok.org.