UNITED STATES DEPARTMENT OF AGRICULTURE 



MISCELLANEOUS PUBLICATION NO. 225 



Washington, D. C. 



Issued July 1935 

 Revised June 1949 



CONVERTING FACTORS AND TABLES 

 OF EQUIVALENTS USED IN FORESTRY 1 



By E. N. Munns, Theresa G. Hoerner, and V. A. Clements, Forest Service 



CONTENTS 



Introduction 



Tables: 



1. Length 



2. Area or surface 



3. Volume and capacity 



4. Weight 



5. Velocity 



6. Power 



7. Weight as applied to length 



8. Weight as applied to area 



9. Weight as applied to volume 



10. Volume of units of weight of water . 



11. Weight of units of volume of water 



12. Rainfall per unit area 



13. Reservoir capacity 



14. Discharge or flow of water 



15. Forest products in board feet 



16. Equivalents of forest products 



17. Area of squares 



18. Basal area of small circles 



19. Area of large circles 



20. N umber of trees per acre 



21. Grade percent 



22. Degree of slope 



23. Beaufort wind scale velocities 



24. Relative humidity 



25. Quarter girth units 



26. Natural trigonometric functions. .. 



27. International log rule 



Page 

 1 



2 



3 

 3 



4 

 4 



5 

 5 

 5 

 6 

 6 

 7 

 7 

 7 



Tables— Continued 



28. Scribner decimal C log rule. 



29. Solid cubic contents of logs_ 

 30. 

 31. 

 32. 

 33. 

 34. 

 35. 



Page 



17 



18 



Comparison of log rules 19 



Ratios for customary map scales 20 



Vertical aerial photo scale relations 20 



Number of seeds per unit weight 21 



Number of seeds per unit area 21 



Discharge second-feet— gallons 22 



36. Runoff gallons— second-feet 22 



37. Runoff acre-feet— gallons 22 



38. Runoff gallons— acre -feet 22 



39. Discharge second-feet— runoff acre-feet _. 23 



40. Discharge second-feet— runoff inches 23 



41 . Inches depth to cubic measure 23 



42. Random numbers 24 



Text figures: 



Temperature, figure 1 28 



Length, figures 2-3 29-30 



Area, figures 4-7 31-34 



Volume, figures 8-10- 



Weight, figure 11 



Power, figure 12 



Wood volume, figure 13 



Wood volume and basal area, figures 14-15_ 



Weight per unit area, figure 16 



Volume and weight, figure 17 



Discharge or flow of water, figure 18 



Values per unit area, figure 19 



Coefficients of correlation, figure 20 



Equivalent rates of runoff, figure 21 



35-37 



40 



41-42 



43 



44 



45 

 46 



47 

 48 



INTRODUCTION 



The increasing use of metric measurements in the natural sciences 

 is causing considerable confusion and difficulty in interpreting data. 

 This is particularly marked in forestry where not only are direct 

 measurements involved, but these measurements are also applied to 

 different units of area. Thus while the conversion of centimeters to 

 inches is a relatively simple matter, the conversion of board feet per 

 acre to cubic meters per hectare is fraught with difficulties which are 

 further increased when monetary values are involved. The purpose 

 of this handbook is to provide members of the Forest Service with 

 conversion factors and forest measurements that are more or less fre- 

 quently encountered in forestry literature. These are expressed in 

 tabular form where it appears most advantageous to do so; in the 



1 This revision corrects certain errors contained in previous issues. 



