Specific Gravity to Molarity Converter
Convert specific gravity (SG) and mass percent into molarity (mol/L), convert molarity back to SG and mass percent, find the solute mass needed to prepare a target solution by volume, and solve stock-to-working SG dilutions, all with step-by-step working.
Select a calculation, choose a water reference, pick a solute preset if you like, then enter the known values.
Molarity
Formula used: Molarity (M) = (10 × mass% × SG × ρ(ref)) ÷ molar mass
1.835
Specific gravity
1.835 g/mL
Density
98% w/w
Mass percent
18.335 mol/L
Molarity
SG → Molarity Hydrometer Visual
A hydrometer-style view of the entered specific gravity, alongside the same solution's molarity.
Step-by-Step Specific Gravity to Molarity Conversion
Here's exactly how this answer was calculated, one step at a time.
Given: SG = 1.835, mass% = 98, molar mass = 98.08 g/mol
Step 1: Convert specific gravity into an actual density
Specific gravity is a unitless ratio of the solution's density to a reference density (almost always water), so multiplying it by the reference density recovers a real density in g/mL.
ρ = SG × ρ(ref) = 1.835 × 1 = 1.835 g/mLStep 2: Convert mass % into grams per litre using the density
Mass percent means grams of solute per 100 g of solution. The factor of 10 rescales that into grams of solute per litre once density is applied.
g/L = 10 × 98 × 1.835 = 1,798.3 g/LStep 3: Divide by the molar mass to get molarity
Molarity is moles of solute per litre, so dividing the mass concentration in g/L by the molar mass in g/mol converts mass into moles.
M = 1,798.3 ÷ 98.08Step 4: Report the result
Molarity = 18.335 mol/L (M)
Calculated result:
18.335 mol/L (M)
Specific Gravity to Molarity Converter: Convert SG to mol/L Online
This free specific gravity to molarity converter takes a specific gravity (SG) reading — the kind you get from a hydrometer, a spec sheet, or a bottle label — together with a mass percent concentration, and turns it into molarity (mol/L). It also runs in reverse, turning a molarity back into SG and mass percent, and it can work out the exact solute mass needed to prepare a target-volume solution, or solve a stock-to-working dilution when both the stock and the target are described by specific gravity.
It is built for chemistry students, lab technicians, battery and electroplating technicians, and anyone handed a hydrometer reading who needs that number turned into a usable molar concentration. Pick the calculation you want, choose a water reference, fill in the numbers, and the answer appears instantly with a complete step-by-step breakdown and a list of solutes commonly labelled by specific gravity, so you rarely need to hunt down a molar mass separately.
Why Convert Specific Gravity to Molarity in the First Place?
Specific gravity shows up on a lot of real-world labels and instrument readouts because it can be measured directly with a cheap, simple hydrometer, without needing a balance, a pipette, or any lab-grade equipment. Battery technicians read the specific gravity of sulfuric acid electrolyte to judge a lead-acid battery's charge state. Brewers and winemakers track SG before and after fermentation. Industrial plants monitor brine, plating baths, and process liquids the same way.
Chemistry calculations, though, are built around molarity, because reaction stoichiometry, titration maths, and dosing calculations all run on moles, not on a unitless density ratio. That gap is exactly what this converter closes: it takes the SG reading you already have on hand, combines it with a mass percent value (which is usually available alongside SG on a chart or label), and returns the molarity your calculation actually needs.
The Specific Gravity to Molarity Formula
The formula used by this calculator is: Molarity (M) = (10 × mass% × SG × ρ(reference)) ÷ molar mass, where mass% is the percent concentration by weight, SG is the unitless specific gravity, ρ(reference) is the reference density (almost always water, in g/mL), and molar mass is in g/mol. The calculation runs in two stages: first, specific gravity is converted into an actual density by multiplying it by the reference density, since SG = ρ(solution) ÷ ρ(reference). Second, that density is combined with the mass percent using the same mass-percent-to-molarity relationship used throughout chemistry: M = (10 × mass% × density) ÷ molar mass.
Because most labs use water at or near 4°C, 20°C, or 25°C as the reference, and water's density at those temperatures sits extremely close to 1.000 g/mL, specific gravity and density in g/mL are numerically almost identical for everyday work. This calculator still keeps the reference density as its own selectable field, so the result stays exact rather than approximate, and so it matches whatever reference temperature a lab procedure specifies.
Worked Example: Battery Acid (Sulfuric Acid Electrolyte)
A fully charged lead-acid battery's electrolyte typically has a specific gravity of around 1.265, corresponding to a sulfuric acid concentration of roughly 35-37% (w/w). Using a value of SG 1.265 and 36% mass percent with sulfuric acid's molar mass of 98.08 g/mol, the density comes out to about 1.265 × 1.000 = 1.265 g/mL, and the molarity works out to (10 × 36 × 1.265) ÷ 98.08 ≈ 4.6 mol/L.
That figure lines up with commonly cited values for battery-strength sulfuric acid, which is a useful check that this calculator's formula behaves correctly for real electrolyte readings. It also illustrates why the SG-to-molarity path matters in the field: a technician reading a hydrometer at the battery gets a specific gravity number directly, and this converter turns that field reading into the molar concentration a chemistry reference or calculation actually needs.
Converting Molarity Back to Specific Gravity and Mass Percent
The reverse direction rearranges the same relationship: mass% = (Molarity × molar mass) ÷ (10 × SG × ρ(reference)). This is useful when a procedure specifies a target molarity and a solute's typical specific gravity is known from a reference table, and the missing piece is the mass percent needed to prepare it.
For instance, a 5 mol/L solution of sodium chloride (molar mass 58.44 g/mol) at a specific gravity of about 1.19 converts to a mass percent of roughly (5 × 58.44) ÷ (10 × 1.19 × 1.000) ≈ 24.6% (w/w), which is close to the concentration of a saturated brine. This calculator's molarity mode carries out this exact calculation for any solute, SG, and reference combination.
Understanding Specific Gravity as a Bridge Between Mass and Volume
Specific gravity is a unitless ratio: SG = ρ(solution) ÷ ρ(reference), almost always compared against pure water at a stated temperature. A specific gravity greater than 1 means the solution is denser than water; a value less than 1 means it is lighter. Because SG has no units, it cannot be used directly as a density in a formula that expects g/mL — it first needs to be multiplied by the reference density, which is exactly what this calculator does before running the mass-percent-to-molarity conversion.
This distinction matters most for precision work: the reference density for water is not a fixed constant, since water is densest at 4°C (1.000 g/mL) and becomes slightly less dense as temperature rises, reaching about 0.9982 g/mL at 20°C. For everyday concentrated-acid or brine calculations the difference is small, but for regulated or high-precision applications, picking the correct reference matches the actual standard a procedure calls for.
Getting the Molar Mass Right
Molar mass is the number that actually links grams to moles, so an incorrect value throws off every downstream result. It is found by summing the atomic masses of every atom in the solute's formula — for sulfuric acid (H2SO4), that is two hydrogen atoms, one sulfur atom, and four oxygen atoms, totalling about 98.08 g/mol.
This calculator's quick-fill list covers the solutes most often labelled by specific gravity — battery-grade sulfuric acid, concentrated hydrochloric and nitric acid, sodium hydroxide, brine-forming salts like sodium chloride and calcium chloride, and a couple of common organics like ethanol and sucrose syrup — so a correct molar mass is only a click away in most everyday cases.
Preparing a Solution to a Target Volume Using Specific Gravity
Because specific gravity converts a volume directly into a mass, it is especially convenient for preparing a solution when you know how much finished volume you need. The relationship is: solution mass = volume × SG × ρ(reference), and then solute mass = (target % × solution mass) ÷ 100.
For example, to prepare 1 litre (1,000 mL) of a 20% sulfuric acid solution with a specific gravity of about 1.14, the solution mass works out to 1,000 × 1.14 × 1.000 = 1,140 g, and the solute mass needed is (20 × 1,140) ÷ 100 = 228 g. This calculator's prepare mode runs that exact calculation, then converts the solute mass into moles using the molar mass you supply, so it can also report the equivalent molarity of the batch you just made.
Diluting an SG Stock Solution and Tracking Its Molarity
Diluting a concentrated stock solution down to a weaker working strength is one of the most routine tasks in analytical and industrial chemistry, and specific gravity makes it possible to do the whole calculation from volumes alone, without ever weighing anything. The stock volume is first converted into a mass using its SG, the mass-based dilution law mass₁ × %₁ = mass₂ × %₂ gives the required final mass, and the target SG then converts that final mass back into a final volume.
As an example, diluting 100 mL of 98% sulfuric acid (SG 1.835) down to a 10% working solution (SG about 1.07) needs a final mass of (100 × 1.835 × 98) ÷ 10 = 1,798.3 g, which at the target SG works out to roughly 1,681 mL — meaning about 1,581 mL of solvent gets added. This calculator's dilute mode runs this exact sequence, and reports the molarity of both the stock and the diluted working solution, so a single dilution step gives you the concentration in both systems at once. Because real solutions are not perfectly additive by volume when mixed, lab-critical dilutions should still be made up to the exact target volume in a volumetric flask rather than by adding precisely the calculated solvent amount.
Where Specific Gravity to Molarity Conversion Shows Up
Battery manufacturing and maintenance is one of the most common places this conversion appears, since lead-acid battery electrolyte strength is checked by hydrometer (specific gravity) but modelled chemically using molarity. Industrial and municipal water treatment uses specific gravity to check brine, coagulant, and disinfectant stock strength before dosing calculations convert those readings into molar or mass-based dosing rates.
Food and beverage production (brewing, winemaking, and syrup manufacturing) tracks specific gravity throughout a batch, and occasionally needs that reading converted into a molar concentration for a chemistry-based quality check. Electroplating and metal finishing baths, as well as general analytical and inorganic chemistry labs working with concentrated commercial acids, round out the main use cases — anywhere a hydrometer or density-based instrument is the primary field tool, but a chemistry calculation downstream needs molarity.
Mistakes to Avoid When Converting Specific Gravity to Molarity
The most common mistake is treating specific gravity as if it already were a density in g/mL without multiplying by the reference density. For water-based references near 1.000 g/mL this introduces only a tiny error, but it is still technically incorrect and can compound with other rounding in a multi-step calculation. A second mistake is forgetting that SG alone is not enough to find molarity — a mass percent (or an equivalent concentration figure) is also required, since SG only fixes the density, not how much of that mass is actually solute.
A third mistake is applying the wrong molar mass, particularly when a specific gravity reading could plausibly belong to more than one common reagent at a similar strength. It's also worth remembering that specific gravity itself changes with concentration and temperature, so a single SG-to-molarity conversion is only as accurate as the mass percent and reference temperature paired with it — always cross-check field readings like these against a reference chart or certificate of analysis for safety-critical work.
Specific Gravity to Molarity vs Molarity to Specific Gravity: Keeping the Two Straight
Because this converter runs in both directions, it helps to keep a clear mental model of which formula belongs to which direction. Going from SG and mass % to molarity, you are combining a unitless ratio and a percentage into a small mole-based number, so the calculation multiplies SG by the reference density, multiplies by 10 and by mass %, then divides by the molar mass. Going from molarity to mass % (at a known SG), you are doing the reverse: multiply molarity by molar mass, then divide by 10 times the actual density.
A simple way to sanity-check the direction is to look at the size of the numbers involved. Specific gravity values for most lab and industrial solutions sit somewhere between about 0.8 (light organics) and 1.9 (concentrated sulfuric acid), while molarity values for those same solutions can range from well under 1 mol/L for dilute working solutions up to the high single digits for concentrated stock acids. If a converted answer looks wildly outside that pattern, it's worth double-checking which mode was selected and which values were entered for SG versus mass percent.
Specific Gravity to Molarity Converter FAQ and Quick Reference
To convert SG and mass % to molarity, use Molarity = (10 × mass% × SG × ρ(reference)) ÷ molar mass. To convert molarity back to mass %, use mass% = (Molarity × molar mass) ÷ (10 × SG × ρ(reference)). To prepare a target volume, use solution mass = volume × SG × ρ(reference), then solute mass = (target % × solution mass) ÷ 100. To dilute an SG stock, use mass₂ = mass₁ × %₁ ÷ %₂, then convert the final mass back to a volume using the target SG.
This free specific gravity to molarity converter is meant for study, lab preparation, field estimation, and general reference use in analytical chemistry, battery maintenance, and industrial process monitoring. Always confirm the specific gravity, mass percent, and molar mass you are using against an actual reference chart, certificate of analysis, or calibrated instrument, and verify safety-critical figures with a qualified professional before relying on them.
Frequently Asked Questions
How do you convert specific gravity to molarity?
Multiply the specific gravity by the reference density to get an actual density in g/mL, then use that density with a mass percent value in the standard formula: Molarity = (10 × mass% × SG × ρ(reference)) ÷ molar mass.
What is the formula for specific gravity to molarity?
Molarity (M) = (10 × mass% × SG × ρ(reference)) ÷ molar mass, where SG is the unitless specific gravity, ρ(reference) is usually water's density in g/mL, and molar mass is in g/mol.
Can I convert specific gravity to molarity without a mass percent?
No. Specific gravity only tells you the solution's density relative to water; it does not by itself tell you what fraction of that mass is solute. A mass percent (or an equivalent concentration figure) is needed alongside SG to calculate molarity.
Is specific gravity the same as density?
No. Density has units like g/mL, while specific gravity is a unitless ratio comparing a solution's density to a reference density, almost always water. Multiplying SG by the reference density gives an actual density.
What is the specific gravity of battery acid in molarity?
Fully charged lead-acid battery electrolyte typically has a specific gravity of about 1.265 and a sulfuric acid concentration of roughly 35-37% (w/w), which works out to approximately 4.6 mol/L.
How do I convert molarity back to specific gravity?
Rearranging the formula, at a known mass %, SG = (Molarity × molar mass) ÷ (10 × mass% × ρ(reference)). This calculator's molarity mode solves the related mass-percent form directly.
Why does the reference water density matter?
Specific gravity is only meaningful relative to a stated reference, and water's density changes slightly with temperature — about 1.000 g/mL at 4°C versus 0.9982 g/mL at 20°C. Using the wrong reference introduces a small but sometimes meaningful error, especially for regulated or high-precision work.
How do I dilute a specific-gravity stock solution and track its molarity?
Convert the stock volume to a mass using its SG, apply mass₁ × %₁ = mass₂ × %₂ to find the final mass needed, convert that back to a volume using the target SG, and then convert both the stock and target concentrations to molarity using the solute's molar mass.