Sulfuric Acid Concentration Calculator

20°C is the standard reference temperature used by essentially every published aqueous-density reference, so every table shares a common, comparable baseline. Sulfuric acid density is temperature-sensitive — a hot batch reads less dense than a cold one at the same concentration, and concentrated H₂SO₄ can self-heat significantly on dilution — so a reading taken far from 20°C will be off. For routine dosing and tank checks this table is accurate enough as-is; let the sample cool to room temperature first for a tighter result.

Density is mass per volume with real units (g/cm³). Specific gravity (SG) is a unitless ratio — the acid's density divided by the density of water under a reference condition, here 20°C water at 0.9982 g/cm³. Because water's density is so close to 1, density in g/cm³ and SG end up numerically close, but they aren't the same quantity: a hydrometer marked "SG" or "Baumé" reads a ratio, not grams per milliliter.

For liquids denser than water, °Bé = 145 − (145 / SG), or the other way, SG = 145 / (145 − °Bé). Sulfuric acid has a famous benchmark on this scale: "66° Baumé" oil of vitriol, the historical name for concentrated commercial sulfuric acid, which works out to roughly 94% H₂SO₄ (SG ≈ 1.84) on this page's table. This calculator reports density and SG directly — run either figure through the formula above if you need to match an old Baumé-labeled chart or tank gauge.

This is a real, repeatable property of the H₂SO₄/water system, not a data error. Near the top of the concentration range, the small amount of remaining water is tightly bound to H₂SO₄ molecules through hydrogen bonding, which packs the mixture unusually dense; as the last bit of water is removed heading toward 100%, that packing effect fades and pure H₂SO₄ itself is slightly less dense than the near-100% hydrated mixture. The result is a density curve that rises, peaks around 97 wt% (≈1.8364 g/cm³ at 20°C), and then eases back down to 1.8305 g/cm³ at 100%.

Because density peaks and then declines, a density value between roughly 1.8305 and 1.8364 g/cm³ sits on the curve twice — once on the way up (below the peak) and once on the way back down (above the peak). Rather than silently guessing which side you meant, the calculator solves both branches and shows both answers when this happens. If you know roughly what concentration to expect (freshly diluted stock acid is almost always below the peak; a near-fuming, highly concentrated batch is more likely above it), pick the branch that matches. When it truly matters, confirm with an independent check such as titration.

Linear interpolation between two closely spaced, independently measured points tracks the true curve closely — the error from treating a short segment as a straight line is far smaller than typical field-measurement error. This table steps in 1-percentage-point increments across the full 0–100% range, which is tight enough for process dosing, tank inventory, and QC; for certified analytical results, confirm with a lab titration.