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ASTM D792 is the ASTM International test method for measuring the density and specific gravity (relative density) of solid plastics by displacement. Test Method A weighs the specimen in water; Test Method B uses liquids other than water. The edition currently listed as active on ASTM’s store is D792-20, last updated 29 July 2020.
Definition and scope
The full title is Standard Test Methods for Density and Specific Gravity (Relative Density) of Plastics by Displacement. Scope clause 1.1 of the current edition states that the test methods describe the determination of the specific gravity (relative density) and density of solid plastics. The title uses the plural “Test Methods” because the document contains two of them, set out in clauses 1.2.1 and 1.2.2 (ASTM store listing for D792-20).
The standard’s own rationale (clause 5.1) is that the specific gravity or density of a solid is a property that is conveniently measured to identify a material. In laboratory terms, D792 is a materials-identification and quality-comparison measurement, not a performance test: it tells you how dense a plastic specimen is, which is then compared with a specification or a previous lot.
How it is used in practice
Displacement methods work from the principle that a solid immersed in a liquid is buoyed up by the weight of liquid it displaces. Testing laboratories that offer D792 describe the measurement in the same terms: the specimen is weighed in air, then weighed again while immersed, and the specific gravity is calculated from the two readings (description from a commercial testing laboratory, Geocomp). Specimen size, number of specimens, immersion liquid temperature and the calculation itself are set out in the standard’s paywalled body, and any laboratory-specific specimen quantity quoted by a testing service is that service’s own requirement rather than the standard’s.
This is why the method matters to equipment decisions: it needs a balance able to weigh a specimen both in air and while it is immersed, so the weighing arrangement has to allow for that second reading. The standard text, not a vendor page, defines the exact requirements, so anyone setting up the test should work from a licensed copy of the current edition.
Method A versus Method B
Test Method A: solid plastics in water
Clause 1.2.1 describes Test Method A as “for testing solid plastics in water.”
Test Method B: solid plastics in liquids other than water
Clause 1.2.2 describes Test Method B as “for testing solid plastics in liquids other than water.” The standard therefore provides for a second immersion liquid when water is not suitable for the material being tested.
D792 compared with related methods
The checklist below sets D792 beside the related methods that the standard’s own wording points to. Each row is limited to what the cited ASTM store listing states, and the 1998 notes are attributed to that historical edition, not to the current one.
| If your material or question is… | What the sources say | Source |
|---|---|---|
| Solid plastic, immersion in water | D792 Test Method A | D792-20, clause 1.2.1 |
| Solid plastic that needs a liquid other than water | D792 Test Method B | D792-20, clause 1.2.2 |
| Sheets, rods, tubes or molded items | The 1998 edition of D792 names these forms in its scope clause 1.1 | D792-98, clause 1.1 (historical edition) |
| Films and sheeting | The 1998 edition’s Note 1 says Test Method D1505 may alternatively be applied to many such forms, as well as to films and sheeting | D792-98, Note 1 (historical edition) |
| A requirement written to ISO 1183 | The 1998 edition’s Note 2 says the standard is not equivalent to ISO 1183 Method A | D792-98, Note 2 (historical edition) |
The practical lesson is that a result generated under D792 should not be treated as interchangeable with an ISO 1183 Method A result simply because both report density. If a customer specification names a particular standard and method, the report should name the same one.
Where it matters for labs, clinics and supply decisions
- Check the edition cited. ASTM’s store lists D792-20 as the active designation, and older editions such as D792-98 remain visible as historical listings with different wording. A specification that cites an older edition should be read against that edition.
- Match method letter to material. Reports should state whether Method A or Method B was used, since the immersion liquid differs.
- Know what the balance must do. Because the method weighs in air and immersed, the balance and its setup have to support both readings. See the CASRAI guides on what an analytical balance is and on analytical balance calibration and weighing technique.
- Keep the measurement within a controlled procedure. A laboratory that runs this test can document it as a standard operating procedure (SOP) tied to the cited edition, and keep the balance on a calibration schedule (what calibration is).
Common misunderstandings
“D792 is the same as ISO 1183.”
The 1998 edition of D792 states that it is not equivalent to ISO 1183 Method A. Compare the current editions of both before treating results as interchangeable.
“D792 covers every plastic form.”
The scope is solid plastics. The 1998 edition itself points to D1505 for many forms, including films and sheeting.
“Density and specific gravity are different tests.”
Clause 1.1 treats both as outcomes of the same method: the standard describes determining the specific gravity (relative density) and density of solid plastics.
“A vendor’s specimen quantity is the standard’s requirement.”
A testing service may ask for a particular number or size of specimens. That is the service’s submission rule, not a clause of D792.
FAQ
What is ASTM D792 used for?
It determines the specific gravity (relative density) and density of solid plastics by displacement. The standard describes this property as one that is conveniently measured to identify a material.
What is the difference between Method A and Method B in ASTM D792?
Method A tests solid plastics in water; Method B tests them in liquids other than water.
Is ASTM D792 still current?
ASTM’s store lists D792-20 as the active edition, last updated 29 July 2020 (store listing checked 29 October 2026). Check the store for any later revision before citing it.
Can ASTM D792 be used for films?
The 1998 edition says Test Method D1505 may be applied to many forms, as well as to films and sheeting. Read the current scope before choosing a method for thin films.
Where can I read the full ASTM D792 text?
The full standard is sold by ASTM International; the store page shows the title, designation and scope.
For wider context on plastics in the lab, see CASRAI’s guides on chemical resistance of plastics and polymer science.
Sources
- ASTM International, D792-20 Standard Test Methods for Density and Specific Gravity (Relative Density) of Plastics by Displacement, store listing (scope and abstract): https://store.astm.org/d0792-20.html, date checked: 29 October 2026.
- ASTM International, D792-98 (historical edition), store listing: https://store.astm.org/d0792-98.html, date checked: 29 October 2026.
- Geocomp, testing service description of D792: https://www.geocomp.com/tests/standard-test-methods-for-density-and-specific-gravity-relative-density-of-plastics-by-displacement/, date checked: 29 October 2026.
