ASTM D792 – Density and Specific Gravity of Plastics by Displacement
ASTM D792 is a standard test method for determining the density and specific gravity of plastics by displacement. A specimen is weighed in air, then weighed again while immersed in water. The buoyant force gives the specimen’s volume, and density is its mass divided by that volume. Specific gravity compares that density to the density of water. The result is a quick, repeatable way to check whether two plastic parts or batches are really the same material.Watch: ASTM D792: Is It the Same Plastic? (Density & Specific Gravity)
Watch the 53-second version: ASTM D792 in a Short
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How to read a density or specific gravity result
- Density is mass per unit volume. Specific gravity compares that density to water, so for plastics tested by water displacement the two numbers are nearly equal.
- Same look does not mean same material. Two parts that look identical can have different densities, which points to a different resin, filler content, or formulation.
- Results are only comparable under the same test conditions. Check the method, immersion fluid, and temperature before comparing two values.
- Density and specific gravity are identity and quality-control checks. They do not predict final part strength or service life on their own. When requesting the test, specify ASTM D792 and note the part’s intended material and application.
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