Our API scale hydrometers measure the scale which was selected in 1921 by the American Petroleum Institute (API), the U.S. Bureau of Mines, and the National Institute of Standards and Technology (NIST) as the standard hydrometer scale for petroleum products.
The API scale is based on the following formula: °API @ 60°F = 141.5/(Specific Gravity @ 60°F) - 131.5
The thermometer scale (where applicable) for these thermo-hydrometers is located in the body. All instruments are suitable for certification for use as a primary reference with NIST traceability.
Specifications Chart
| Item No. | API Range | ASTM No. | Thermometer Range | Thermometer Liquid Fill | Length |
| 6751HTS | -1 to 11° | 51H | 0 to 150°F | Safety Blue | 15 in. (380 mm) |
| 6752HTS | 9 to 21° | 52H | 0 to 150°F | Safety Blue | 15 in. (380 mm) |
| 6753HTS | 19 to 31° | 53H | 0 to 150°F | Safety Blue | 15 in. (380 mm) |
| 6754HTS | 29 to 41° | 54H | 0 to 150°F | Safety Blue | 15 in. (380 mm) |
| 6755HTS | 39 to 51° | 55H | 0 to 150°F | Safety Blue | 15 in. (380 mm) |
| 6756HTS | 49 to 61° | 56H | 0 to 150°F | Safety Blue | 15 in. (380 mm) |
| 6757HTS | 59 to 71° | 57H | 0 to 150°F | Safety Blue | 15 in. (380 mm) |
| 6758HTS | 69 to 81° | 58H | 0 to 150°F | Safety Blue | 15 in. (380 mm) |
