SG · Baumé · API · Brix

Specific gravity converter: lb/gal, Baumé, API, and Brix

Read the supplier's density in whatever unit their sheet uses.

Last updated 2026-09-27. Math runs in your browser, no data leaves your computer.

Enter the figure exactly as it appears on the SDS, certificate of analysis, or tank ticket, and pick its unit. Everything else on the sheet is then one glance away.

Copy the number with all its decimals, because the third decimal of an SG is often the one a spec turns on.

Liquids heavier than water read on the heavy Baumé scale and lighter ones on the light scale, and the COA should say which one it used.

This only moves the density rows, by at most 0.2 percent. The water values come from the USGS water density table for 4 °C and 60 °F, and from NBS Circular 440 for 20 °C.

Before the booking, screen the name on the invoice. Shipment pre-check is on the paid plans, from USD 59 a month.

General guidance only. Verify against the cited primary sources before you commit to a shipment, declaration, or contract.

Where each formula comes from

Specific gravity is the ratio of a liquid's density to the density of water, both at stated temperatures, so it has no unit. Turning it into a density means multiplying by the density of water at the reference temperature: 1.00000 g/cm³ at 4 °C and 0.99907 g/cm³ at 60 °F in the USGS table, or 0.99823 at 20 °C in NBS Circular 440. From g/mL the rest is unit arithmetic, with kg/m³ equal to g/mL × 1,000 and lb/gal equal to g/mL × 8.3454 from the NIST Handbook 44 gallon and pound.

The Baumé scales are the ones fixed by the Bureau of Standards in NBS Circular 59 (1916). For liquids heavier than water, °Bé = 145 − 145 / SG, which inverts to SG = 145 / (145 − °Bé); for liquids lighter than water, °Bé = 140 / SG − 130, which inverts to SG = 140 / (130 + °Bé). Both use SG at 60/60 °F, and water sits at 0 on the heavy scale and at 10 on the light one.

API gravity works like the light Baumé scale with different constants. The EIA glossary gives it as °API = 141.5 / SG − 131.5 at 60/60 °F, so SG = 141.5 / (°API + 131.5), and the scale runs backwards: the higher the API number, the lighter the liquid.

Brix is grams of sucrose per 100 g of solution, and there is no exact closed formula for it. The tool looks the SG up in NBS Circular 440 Table 109, which lists SG at 20/20 °C for every tenth of a degree Brix from 0 to 100, and interpolates between the 21 rows at 5 degree steps that it carries. Those rows run from SG 1.00000 at 0 °Brix to 1.55454 at 100 °Brix, and anything outside that band is reported as out of range rather than extrapolated.

Worked example: a 66 °Bé acid against an SG spec

The booking. Your purchase spec for sulfuric acid reads SG 1.835 minimum at 60/60 °F, and the supplier quotes it as 66 °Bé. On the heavy scale, 145 / (145 − 66) = 1.8354, which clears the spec, and the contract is signed on the Baumé figure, which looks fine on paper.

The failure. The first COA reads 65.8 °Bé, which the supplier treats as 66 within tolerance. Run it through the same formula and 145 / (145 − 65.8) = 1.8308, below your 1.835 floor, so receiving QC holds the tank while two sides argue over which unit the spec meant. The choice in front of you is plain: accept the lot off spec, or send it back.

The fix. Write the spec in both units with the same number of decimals, for example 66.0 °Bé minimum, equal to SG 1.8354 at 60/60 °F. The supplier now reads the same floor your QC reads, a 65.8 lot is caught at the plant rather than at your dock, and the next shipment ships to spec.

Need the SG turned into pounds for a purchase order? The gallons to pounds calculator does the weight side at /tools/chemicals/gallons-to-pounds-calculator.

SG shifts with temperature, and a tank loaded hot weighs less per gallon. The density at temperature calculator corrects for that at /tools/chemicals/density-at-temperature-calculator.

Frequently asked

How do I convert specific gravity to pounds per gallon?

Multiply the SG by 8.3454, which is the weight in pounds of one US gallon of a liquid at 1.000 g/mL. The factor follows from NIST Handbook 44, where the gallon is 3.785411784 liters and the pound is 0.45359237 kilograms. An SG of 1.20 is 1.20 × 8.3454 = 10.01 lb per gallon.

What is the difference between the heavy and light Baumé scales?

They are two separate scales that meet at water. The heavy scale covers liquids denser than water, with SG = 145 / (145 − °Bé), so water reads 0 °Bé and a 66 °Bé acid is SG 1.8354. The light scale covers liquids lighter than water, with SG = 140 / (130 + °Bé), so water reads 10 °Bé. Both formulas and the 60/60 °F reference come from NBS Circular 59 of 1916, which fixed the United States standard Baumé scales.

How is API gravity calculated?

Degrees API = 141.5 / SG − 131.5, with SG measured at 60/60 °F. That is the definition in the EIA glossary and in the API and ASTM petroleum methods. Water comes out at 10 °API; a lighter oil reads higher, so 35 °API is SG 0.8498.

How accurate is the Brix figure?

It is a lookup, not a formula. The tool interpolates between the 5 degree steps of NBS Circular 440 Table 109, which lists SG at 20/20 °C for pure sucrose solutions from 0 to 100 °Brix. For a sugar syrup the result lands within about 0.03 °Brix of the full table; for a juice, molasses, or anything with salts or acids dissolved in it, treat it as an estimate and use a refractometer for the spec.

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