Calculates Shelf Sag
The Sagulator helps you design shelves by calculating
shelf sag (deflection) given type of shelf material, shelf load, length, width, and
thickness. See the notes below for usage tips.
1. The eye will notice a deflection of 1/32 inch per
running foot, or 3/32" (0.09") for a 3' wide bookshelf.
2. Once you have a maximum allowable sag figure in mind, you can
design your shelf by tweaking the material types and dimensions. Many bookshelves have a
depth of 8" to 12", a width of 24" to 36", and a thickness of
3/4" to 1".
3. A fully loaded bookshelf weighs 20-25 pounds (9-11 kg) per running
foot, or 60-75 pounds (27-34 kg) for a 3' wide shelf.
4. You can enter fractional dimensions as decimals (8.75), or as
conventional fractions (8 3/4). If you use fractions, just make sure to leave a space
between any leading whole number and the fraction.
5. This calculator can also be used to measure beam deflection. You
can specify either center or uniform loading along the length of the beam.
6. The deflection calculations are based on average wood stiffness
properties measured in controlled laboratory conditions (U.S. Forest Products Lab). Your
mileage may vary.
Thanks to Harry A. "Steve" Stephenson, Autocad Operator, with H & H
Associates, Inc. in Nashville, TN for providing advice and formulas. Another very
helpful resource was Bruce Hoadleys book - Understanding Wood:
A Craftsman's Guide to Wood Technology.