How do you calculate the weight of a balsa stick?

Short answer: multiply the stick's volume by the wood's density. Volume is width × thickness × length, and hobby balsa is typically about 0.10 to 0.20 g/cm³.

Steps

1. Work in centimetres. 1 in = 2.54 cm.
2. Volume (cm³) = width × thickness × length.
3. Weight (g) = volume × density (g/cm³).

Worked example

A 1/8 in square stick, 36 in long, at a density of 0.15 g/cm³:

• Width and thickness = 0.3175 cm. Length = 91.44 cm.
• Volume = 0.3175 × 0.3175 × 91.44 ≈ 9.2 cm³.
• Weight = 9.2 × 0.15 ≈ 1.4 g.

The same stick at 0.10 g/cm³ weighs about 0.9 g, and at 0.20 g/cm³ about 1.8 g. That spread is why weighing and sorting sticks pays off.

Plan the mass of a bridge

1. List every member with its length and cross-section.
2. Add up the lengths for each section size, and compute the weight of each.
3. Add glue, roughly a few milligrams per joint.
4. Compare with the mass limit before you cut anything.

Real sticks vary, so weigh the actual pieces as you go. See weighing accurately.