|MadSci Network: General Biology|
A good source for this would be: The Allometry of Growth and Reproduction M.J. Reiss Cambridge University Press Cambridge, UK 1989 (1991 paperback) ISBN 0 521 42358 9 There's a lot of material here but on p. 59 of the paperback version, Reiss cites Hemmingsen's analysis of metabolic rates for homeotherms, poikilotherms and unicellular organisms. Of particular note is the equation for poikilotherms: BMR= 0.144*(W**0.738) where BMR is in cubic centimetres of oxygen per hour and W is body weight in grams. I hope this helps.
Try the links in the MadSci Library for more information on General Biology.