Balsa wood movement, board-foot & weight calculator
- Janka
- —
- Density
- 11.2lb/ft³
- T/R ratio
- 2.5
- Spec. gravity
- 0.16
Balsa (Ochroma pyramidale) is an imported species. It has a specific gravity of 0.16, and an air-dry density near 11 lb/ft³ (179 kg/m³) (mechanical values at 12% moisture content). It shrinks 7.6% tangentially and 3% radially from green to oven-dry (T/R ratio 2.5), so a 12-inch flatsawn board moves about 0.18 in (≈ 3/16 in) across a 6-point moisture swing (about 6%→12% MC).
Compute Balsa: movement, weight & board footage
Every number below is worked from Balsa's own shrinkage and density figures, not looked up from a table — change the width, moisture swing, or board size in the calculators linked alongside.
Cross-grain movement by board width
| Board width | Flatsawn (tangential) | Quartersawn (radial) |
|---|---|---|
| 2″ | 0.03″ (≈ 1/32 in) | 0.012″ (≈ 0 in) |
| 3″ | 0.046″ (≈ 1/32 in) | 0.018″ (≈ 1/32 in) |
| 4″ | 0.061″ (≈ 1/16 in) | 0.024″ (≈ 1/32 in) |
| 6″ | 0.091″ (≈ 3/32 in) | 0.036″ (≈ 1/32 in) |
| 8″ | 0.122″ (≈ 1/8 in) | 0.048″ (≈ 1/16 in) |
| 10″ | 0.152″ (≈ 5/32 in) | 0.06″ (≈ 1/16 in) |
| 12″ | 0.182″ (≈ 3/16 in) | 0.072″ (≈ 1/16 in) |
| 16″ | 0.243″ (≈ 1/4 in) | 0.096″ (≈ 3/32 in) |
Need a different width or moisture swing? Run the movement calculator preloaded with Balsa. At a T/R ratio of 2.53, Balsa is unstable — it moves far more tangentially than radially, the pattern behind cupped tabletops and opened joints — quartersawn stock and generous allowance for seasonal movement matter here.
Board footage & weight, standard sizes
| Nominal size × length | Board feet | Weight |
|---|---|---|
| 1×4 × 8′ | 2.67 bd ft | 2.5 lb |
| 1×6 × 8′ | 4 bd ft | 3.7 lb |
| 1×8 × 8′ | 5.33 bd ft | 5 lb |
| 1×10 × 8′ | 6.67 bd ft | 6.2 lb |
| 1×12 × 8′ | 8 bd ft | 7.5 lb |
| 2×4 × 8′ | 5.33 bd ft | 5 lb |
| 2×6 × 8′ | 8 bd ft | 7.5 lb |
| 2×8 × 8′ | 10.67 bd ft | 10 lb |
Different length or size? Run the board foot calculator or the weight calculator, both preloaded with Balsa.
Seasonal movement by city
| City | Driest month (EMC) | Most-humid month (EMC) | EMC swing | 12″ board movement |
|---|---|---|---|---|
| Phoenix, AZ | Jun · 4.4% | Dec · 9% | 4.6 pts | 0.14″ (≈ 1/8 in) |
| Chicago, IL | May · 12.3% | Dec · 15.1% | 2.8 pts | 0.085″ (≈ 3/32 in) |
| Miami, FL | Apr · 12.2% | Sep · 14.4% | 2.2 pts | 0.067″ (≈ 1/16 in) |
| Boston, MA | Apr · 11.5% | Sep · 12.8% | 1.3 pts | 0.04″ (≈ 1/32 in) |
| Denver, CO | Jul · 8% | Dec · 10.5% | 2.5 pts | 0.076″ (≈ 1/16 in) |
| Seattle, WA | Jul · 12% | Dec · 16.9% | 4.9 pts | 0.149″ (≈ 5/32 in) |
Driven by Balsa's tangential shrinkage of 7.6%. These are outdoor equilibrium-moisture figures, so they are an upper bound — a climate-controlled interior swings less. How this is calculated.
How Balsa compares
Ranked against the 196 species in the Wood Handbook tables this site carries.
- Weight: at 11.2 lb/ft³ it is heavier than 0% of the 170 species measured — an 8-foot 1×6 board weighs about 3.7 lb.
- Stability: its T/R ratio of 2.53 is more even than 2% of the 196 species here — as humidity changes, 98% of them hold their shape more evenly.
See Balsa plotted against every species we carry: the full density chart .
About Balsa
Balsa (Ochroma pyramidale) is widely distributed throughout tropical America from southern Mexico to southern Brazil and Bolivia, but Ecuador has been the principal source of supply since the wood gained commercial importance. It is usually found at lower elevations, especially on bottom-land soils along streams and in clearings and cutover forests. Today, it is often cultivated in plantations. Several characteristics make balsa suitable for a wide variety of uses. It is the lightest and softest of all woods on the market. The lumber selected for use in the United States weighs, on the average, about 180 kg m–3 (11 lb ft–3) when dry and often as little as 100 kg m–3 (6 lb ft–3). The wood is readily recognized by its light weight, nearly white or oatmeal color, often with a yellowish or pinkish hue, and its unique velvety feel. Because of its light weight and exceedingly porous composition, balsa is highly efficient in uses where buoyancy, insulation against heat or cold, or low propagation of sound and vibration are important. Principal uses are for life-saving equipment, floats, rafts, corestock, insulation, cushioning, sound modifiers, models, and novelties.
Durability & sustainability
Decay resistance: the Wood Handbook rates Balsa heartwood slightly or nonresistant to fungal decay . Ratings are for heartwood only and the table's own note cautions that resistance varies substantially within a species; treat this as a general indicator, not a guarantee, especially for ground contact. Wood Handbook, Chapter 14: Biodeterioration of Wood (Arango, Lebow, Glaeser), USDA Forest Products Laboratory, FPL-GTR-282 (2021), Table 14-1. Public domain.
Properties
| Specific gravity | 0.16 |
|---|---|
| Janka hardness (side) | — |
| Density (air-dry, 12% MC) | 11.2 lb/ft³ (179 kg/m³) ovendry-weight basis: 10 lb/ft³ |
| Weight per board foot (air-dry) | 0.93 lb |
| Radial shrinkage (green→oven-dry) | 3% |
| Tangential shrinkage (green→oven-dry) | 7.6% |
| Volumetric shrinkage (green→oven-dry) | 10.8% |
| T/R ratio (stability indicator) | 2.5 |
Shrinkage is total green-to-oven-dry (Table 4-4); strength values are at 12% MC. Full bases and the derivation formulas are on the methodology page. Values shown as “—” have no matched entry in the Wood Handbook strength tables (5-3b/5-5b).
Data: USDA Forest Products Laboratory, Wood Handbook FPL-GTR-282 (2021), public domain.