What is Specific Gravity?
Specific gravity (SG) tells you how dense wood is by comparing it to water. Water has an SG of 1.00. Wood lighter than water (SG < 1.0) floats; wood heavier than water (SG > 1.0) sinks. Most woods range from 0.10 (balsa) to 1.30 (lignum vitae).
Why It Matters
Predicts Key Properties
- Strength: Denser wood is generally stronger.
- Hardness: Higher SG correlates with higher Janka hardness.
- Workability: Very dense woods dull tools faster but take a superb polish.
- Fuel value: Denser wood produces more heat per volume.
- Shrinkage: Denser woods shrink and swell more with moisture changes.
Costa Rican Examples
| Species | SG | Classification | | ------------ | ---- | --------------- | | Balsa | 0.10 | Extremely light | | Laurel | 0.42 | Light | | Cedro Amargo | 0.47 | Medium-light | | Teca | 0.55 | Medium | | Guapinol | 0.76 | Heavy | | Cocobolo | 1.10 | Very heavy | | Nazareno | 0.91 | Heavy |
Practical Applications
- Construction: Medium SG woods (0.40–0.60) balance strength and weight for structural framing.
- Fine furniture: High SG woods (0.70+) take detailed carving and polishing.
- Firewood: Higher SG burns longer and produces more energy.
- Flooring: High SG required for durability underfoot.
Measurement
Specific gravity is measured by weighing an oven-dried sample and dividing by the weight of an equal volume of water. In Costa Rica, the standard reference is green volume / oven-dry weight.