Hydrochloric 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. HCl density is temperature-sensitive — a hot sample reads less dense than a cold one at the same concentration — so a reading taken far from 20°C will be off by a small, predictable amount. For routine dosing and tank checks this table is accurate enough as-is; let the sample reach room temperature first if you need 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 for aqueous acids, but they aren't the same quantity: a hydrometer marked "SG" reads that ratio directly, not grams per milliliter.

For liquids denser than water, Baumé and specific gravity convert with °Bé = 145 − (145 / SG), or the other way, SG = 145 / (145 − °Bé). Muriatic acid (technical-grade HCl) has historically been sold by Baumé strength — 20° Baumé is a common commodity grade, working out to roughly 31–32% HCl. This calculator reports density and SG directly; run either figure through the formula above if you need to match a Baumé-labeled drum or an older chart.

That figure is a rounded commercial convention that has circulated for decades on drum labels and safety sheets, not a precise lab value. Interpolating this page's 20°C reference table at exactly 37.00% gives roughly 1.184 g/cm³ — noticeably below 1.19. The gap comes from a mix of things: some historical figures were taken at a warmer reference temperature (density rises somewhat as temperature drops), some are simply rounded for a shipping label, and "37%" itself is sometimes used loosely for concentrated technical-grade acid that isn't exactly 37.00% w/w. Use this calculator's interpolated value, not the rounded commercial figure, when the exact number matters.

40% w/w is close to the practical ceiling for aqueous HCl at room temperature — beyond that, HCl gas begins to come out of solution (it "fumes") rather than staying dissolved, and commercially available concentrated hydrochloric acid tops out in the 37–38% range for exactly this reason. There is no meaningful 45% or 50% HCl solution to look up at 20°C and atmospheric pressure, which is why the reference data doesn't extend further.

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 from a hydrometer or refractometer. This table steps in roughly 0.005 g/cm³ density increments, which is tight enough for process dosing and QC; for certified analytical results, confirm with a lab titration.