Boehm, Barry, et al. Software Cost Estimation with Cocomo II. Reading, MA: Addison Wesley, 2000. The Cocomo II estimation model described in this book provides formulas for converting size estimates in lines of code into effort. Keep in mind the warnings about the "control knobs" involved.
ISBSG. Practical Project Estimation, 2nd Edition: A Toolkit for Estimating Software Development Effort and Duration. Victoria, Australia: International Software Benchmarking Standards Group, February 2005. This book contains numerous useful formulas for computing effort estimates from size estimates. The book is refreshingly candid about the accuracy of its formulas; it includes sample size and r-squared values you can use to assess the validity of its formulas.
Putnam, Lawrence H. and Ware Myers. Measures for Excellence: Reliable Software On Time, Within Budget. Englewood Cliffs, NJ: Yourdon Press, 1992. The Putnam model described in this book converts size estimates in lines of code into effort.