Foam wedges can be used to support the back when lying in bed. They are rested on top of the mattress and are available in a range of sizes with various angles of elevation.
To find what size foam wedge you need to achieve a 30-degree head elevation angle, use a calculator and a trigonometry formula, or choose from the examples of suggested dimensions in Section 4.
Wedges have two right-angled triangle faces. This means that trigonometry (mathematical rules for right-angled triangles) can be used to calculate the angle of elevation if you know the height and length of the wedge.
If the height divided by the length equals 0.577, then the angle of elevation of the head will be 30 degrees. If the height divided by the length is less than 0.577, then the angle of elevation of the head will be smaller than 30 degrees.
If the height divided by the Length is closer to 0.700 then the angle of elevation of the head will be closer to 35 degrees.
If you know what length wedge you want, you can also use trigonometry to calculate how high the wedge should be. Multiply 0.57735 by the length to find the height you will need. Similarly, if you know how high you want the wedge, then you can calculate the length. The height divided by 0.577735 equals the length.
Some examples of wedge sizes that will give you a 30-degree elevation are 20 inches long by 11.5 inches high; 22 inches long by 12.5 inches high; and 24 inches long by 14 inches high.