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The thickness of plywood has a significant effect on its ability to resist bending or breaking under load. When a piece of plywood has double the thickness of another, its bending resistance increases by a factor of eight.
Any DIY ramp being used for wheelchairs should use ¾" (19 mm) or greater thickness plywood as it offers superior strength to thinner plywood.
| Table: bending resistance relative to ¼" plywood | |||
|---|---|---|---|
| Thickness (inches) | Thickness (mm) | Relative Bending Resistance | |
| 1/4 | 0.25 | 6.350 | 1 |
| 3/8 | 0.375 | 9.525 | 3.375 |
| 1/2 | 0.5 | 12.700 | 8.000 |
| 5/8 | 0.625 | 15.875 | 15.625 |
| 3/4 | 0.75 | 19.050 | 27.000 |
| 7/8 | 0.875 | 22.225 | 42.500 |
| 1 | 1 | 25.400 | 64.000 |
| It can be seen in this table that ¾"-thick plywood has 27 times the bending resistance of ¼"-thick plywood. | |||
Stacking plywood sheets to increase strength is not recommended. Two stacked sheets do not provide double the strength of a single sheet.