Concentration converter

It moves a lab result from one unit to another without arithmetic slips: ppm, mg/L, % by weight, molarity, normality, meq/L and mg/L as CaCO₃. It helps compare reports from different labs, check regulatory limits and feed other calculations such as scaling indices and chemical dosing.

Only for water and dilute solutions. ppm is mass per mass (mg/kg) and mg/L is mass per volume; they match when 1 liter weighs 1 kg. In a brine with a specific gravity of 1.20, 1,000 mg/L is only 833 ppm, a 17% error if the units are mixed up.

Divide by the equivalent weight of calcium (40.078 ÷ 2 = 20.04) to get meq/L and multiply by 50.04. In the page example, 100 mg/L of Ca²⁺ gives 4.99 meq/L and 249.7 mg/L as CaCO₃ (14.6 grains per gallon), which is how calcium hardness appears on water reports.

Molarity counts moles of substance per liter; normality counts equivalents, that is, moles of H⁺, OH⁻, charge or electrons exchanged. For H₂SO₄, which releases 2 H⁺, a 0.05 M solution is 0.10 N. Normality depends on the reaction, which is why the calculator asks for the valence.

Molar mass comes from the periodic table or the product SDS (sum of the atomic masses in the formula). Solution density comes from the SDS, the supplier certificate or a hydrometer. For water and solutions below 1% to 2% by weight, 1.00 g/mL is good enough.

If the sum of cations in meq/L matches the sum of anions, the analysis is complete and consistent. In the sample list, cations add to 6.90 meq/L and anions to 7.10 meq/L, an error of −1.4%, within the 2% Standard Methods limit for that range. A larger error suggests a missing ion or a wrong result; ask the lab to rerun it.

Using total hardness instead of calcium hardness, forgetting the valence when going to meq/L, treating ppm as mg/L in strong solutions and adding ions in mg/L instead of meq/L. Another one is mixing mg/L of HCO₃⁻ with mg/L as CaCO₃: 244 mg/L of bicarbonate is 200 mg/L of alkalinity as CaCO₃.