UNITED STATES DEPARTMENT OF AGRICULTURE 



MISCELLANEOUS PUBLICATION NO. 225 



Washington, D. C. 



Issued July 1935 

 Revised July 1947 



CONVERTING FACTORS AND TABLES 

 OF EQUIVALENTS USED IN FORESTRY 



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. Number 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 



Tables— Continued 



28. Scribner decimal C log rule 



29. Solid cubic contents of logs 



30. Comparison of log rules 



31 . Ratios for customary map scales 



32. Vertical aerial photo scale relations 



33. Number of seeds per unit weight 



34. Number of seeds per unit area 



35. Discharge second-feet— gallons 



36. Runoff gallons— second-feet 



37. Runoff acre-feet— gallons 



38. Runoff gallons— acre -feet 



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



40. Discharge second-feet— runoff inches 



41. Inches depth to cubic measure 



42. Random numbers 



Text figures: 



Temperature, figure 1 



Length, figures 2-3 



-10. 



Volume, figures 8- 



Weight, figure 11 



Power, figure 12 



Wood volume, figure 13 



Wood volume and basal area, figures 14-15. 



Weight and volume, figure 16 



Volume— weight, figure 17 



Discharge or flow of water, figure 18 



Values per unit area, figure 19 



Coefficients of correlation, figure 20 



E quivalent rates of flow, figure 21 



35-37 

 38 

 39 

 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 



