Short answer: Pounds = gallons × specific gravity × 8.34 lb/gal. EPA’s Tier II instructions give exactly this: density (lb/gal) = specific gravity × 8.34, and pounds = density × gallons on site. The 8.34 is the weight of one U.S. gallon of water, rounded; water at 1.000 g/mL works out to 8.345 lb/gal. Find the specific gravity or density in Section 9 of the SDS. For a mixture, convert the whole product to pounds first, then multiply by the component’s weight percent.
Why the conversion matters
EPCRA thresholds are in pounds: 10,000 pounds for most hazardous chemicals and 500 pounds or the TPQ for Extremely Hazardous Substances (40 CFR 370.10). Tier II range codes are weight ranges in pounds, and Part 370 says: “To convert gas or liquid volume to weight in pounds, multiply by an appropriate density factor” (note to 40 CFR 370.43(a)). The only federal Tier II thresholds stated in gallons are the retail gas station thresholds for gasoline (75,000 gallons) and diesel (100,000 gallons) in compliant underground tanks.
Liquids are bought and stored by volume, in drums, totes, and bulk tanks. So almost every liquid threshold check involves this conversion, and an error in density moves every downstream number with it.
The formula
EPA’s Regulatory Overview and Instructions for the Tier II Form (May 2026) state:
EPA Tier II instructions
Pounds = density (lbs/gal) × gallons on-site
Density = specific gravity × 8.34 (lbs/gal)
Specific gravity, also called relative density, is the ratio of a liquid’s density to the density of water. A product with specific gravity 1.20 weighs 1.20 times as much as the same volume of water. Multiplying by the weight of a gallon of water turns the ratio into pounds per gallon.
Where 8.34 comes from, and the temperature caveat
NIST lists 1 lb/gal (U.S.) as 119.8264 kg/m³. A liquid with a density of exactly 1 g/mL (1,000 kg/m³) therefore weighs 1,000 ÷ 119.8264 = 8.3454 lb per U.S. gallon. Rounded to three significant figures, that is the 8.34 in EPA’s formula.
Water is not exactly 1 g/mL at every temperature. USGS gives water’s density as 1.00000 g/cm³ at 39.2 °F (4.0 °C), 0.99907 at 60 °F (15.6 °C), and 0.99802 at 70 °F (21 °C). In pounds per gallon that is about 8.345, 8.338, and 8.329. The spread across ordinary storage temperatures is about 0.2%.
Two consequences follow. First, 8.34 is a rounded reference value for water, not a precise constant. For threshold screening the rounding is far smaller than the uncertainty in most SDS density and concentration figures. Second, specific gravity is defined against water at a reference temperature. Petroleum practice, as EIA’s definition of API gravity shows, uses 60 °F for both the liquid and the water. When a Section 9 value states its temperature, record it with the number.
Finding density in SDS Section 9
OSHA’s Hazard Communication Standard requires Section 9 of every SDS, “Physical and chemical properties,” to include density and/or relative density among its required properties (29 CFR 1910.1200, Appendix D). Section 9 also carries flash point, which matters for fire code and OSHA PSM screening. What varies is the unit and label. These are the forms you will see and how to turn each into pounds per gallon:
| As written on the SDS | To get lb/gal | Example |
|---|---|---|
| Specific gravity or relative density (water = 1) | Multiply by 8.34 | 1.10 × 8.34 = 9.17 lb/gal |
| Density in g/mL or g/cm³ | Multiply by 8.345 (or 8.34 for screening; 1 g/mL equals 1 g/cm³) | 0.87 g/mL × 8.345 = 7.26 lb/gal |
| Density in lb/gal | Use as is | 9.5 lb/gal |
| Density in kg/m³ | Divide by 119.83 | 1,180 ÷ 119.83 = 9.85 lb/gal |
| Density in kg/L | Same number as g/mL; multiply by 8.345 | 1.18 kg/L × 8.345 = 9.85 lb/gal |
| API gravity (petroleum liquids) | Specific gravity at 60 °F = 141.5 ÷ (°API + 131.5), then multiply by 8.34 | 35 °API: 141.5 ÷ 166.5 = 0.850; × 8.34 = 7.09 lb/gal |
Watch for three things in Section 9. Some SDSs give a range, such as “1.05–1.15.” For a threshold check, using the high end gives the larger weight; that is a conservative practice, not a stated rule. Some give “bulk density” for a solid, which is not a liquid density. And a few give vapor density (relative to air) next to relative density (relative to water); vapor density is not what you want for a liquid in a drum.
Worked examples: single products
Two 1,000-gallon tanks of a product with specific gravity 1.10: 2,000 × 1.10 × 8.34 = 18,348 lb. Above the 10,000-lb threshold.
500 gallons of a solvent, density 0.87 g/mL: 500 × 0.87 × 8.345 = 3,630 lb. Using 8.34 instead gives 3,628 lb; the difference does not matter here.
300 gallons of a product at 1,180 kg/m³: 1,180 ÷ 119.83 = 9.85 lb/gal; 300 × 9.85 = 2,954 lb.
10,000 gallons of a fuel oil at 35 °API: specific gravity 0.850; 10,000 × 0.850 × 8.34 = 70,877 lb.
Mixtures: convert the product, then apply weight percent
For a mixture, Part 370 sets the order of operations: “multiply the concentration of the hazardous chemical component (in weight percent) by the weight of the mixture (in pounds)” (40 CFR 370.14(c)). That means:
- Use the density of the mixture, from the product’s own SDS, to convert gallons of product to pounds of product.
- Multiply pounds of product by the weight percent from SDS Section 3.
Avoid two shortcuts. Taking a percentage of the gallons and multiplying by the pure component’s density only matches the regulation when the SDS percentage is by volume and the mixture behaves ideally, which you rarely know. And using the pure component’s density for the whole product misstates the product weight whenever the other ingredients are lighter or heavier. If Section 3 gives a range, EPA’s guidance is to use the upper bound. See mixtures in Tier II.
Worked example: a component in a mixture
1,200 gallons of a cleaner, relative density 1.15, with a hazardous component listed at 25–35% by weight.
Product weight: 1,200 × 1.15 × 8.34 = 11,509 lb.
Component at the upper bound: 11,509 × 0.35 = 4,028 lb. At the lower bound it would be 2,877 lb.
If the same component is in other products on site, add those amounts on the same day before comparing to the threshold.
Gases and solids
The note to 40 CFR 370.43 covers gases as well as liquids: convert volume to weight with an appropriate density factor. Compressed and liquefied gas cylinders are usually easier to handle by weight from the supplier’s fill data than by volume. Solids are normally bought by weight. For EHS solids, the quantity counted for the TPQ test depends on physical form; see EPCRA 302 EHS and TPQs.
Common questions
How do I convert gallons to pounds for Tier II?
Multiply gallons by the specific gravity from SDS Section 9 and by 8.34 pounds per gallon. EPA’s Tier II instructions give density (lb/gal) = specific gravity × 8.34 and pounds = density × gallons on site.
Why is water 8.34 pounds per gallon?
A U.S. gallon of a liquid at exactly 1 g/mL weighs 8.345 pounds, based on NIST’s conversion of 1 lb/gal to 119.8264 kg/m³. Water is very close to 1 g/mL at ordinary temperatures, and 8.34 is the rounded figure. At 60 °F water weighs about 8.338 lb/gal.
How many pounds is a 55-gallon drum?
It depends on the product’s density. Multiply 55 by the specific gravity and by 8.34. A drum of a product with specific gravity 1.00 holds about 459 pounds; at specific gravity 1.50 it holds about 688 pounds.
How do I convert g/mL or kg/m3 to pounds per gallon?
Multiply g/mL (or g/cm3, or kg/L) by 8.345. Divide kg/m3 by 119.83. Both come from NIST conversion factors.
Should I use the density of the pure chemical or of the product?
Of the product. 40 CFR 370.14(c) calculates a component as its weight percent times the weight of the mixture, so convert the product’s gallons to pounds with the product’s own density, then apply the weight percent.
Where Chemsana fits
Chemsana extracts density and composition from each SDS, converts container volumes to pounds, and totals each CAS number across products with the upper bound used for threshold checks. The conversion and its source are shown alongside each total. See SDS extraction.
Sources
- Regulatory Overview and Instructions for the Tier II Form (May 2026), EPA, “Converting liquid gallons to pounds.”
- 40 CFR 370.43, range codes and note on volume-to-weight conversion, eCFR, accessed October 2026.
- 40 CFR 370.14(c), quantity of a component in a mixture, eCFR, accessed October 2026.
- 40 CFR 370.10, thresholds, eCFR, accessed October 2026.
- 29 CFR 1910.1200 Appendix D, Safety Data Sheets, OSHA, accessed October 2026.
- NIST Guide to the SI, Appendix B.8, conversion factors, NIST, accessed October 2026.
- Water Density, USGS Water Science School, accessed October 2026.
- API gravity, EIA glossary, U.S. Energy Information Administration, accessed October 2026.
This guide summarizes federal requirements for general information. States can set lower thresholds or extra requirements, and it is not legal advice. Confirm obligations with your SERC, LEPC, or a qualified EHS professional.