Concentration - Solution Converter

Kilogram per Liter (kg/L)

Mass concentration in SI units. 1 kg/L = 1,000 g/L = 1,000,000 mg/L. Commonly used for concentrated industrial solutions and aqueous systems.

Advantage: Direct relationship between mass of solute and solution volume. For dilute aqueous solutions, numerically similar to specific gravity.

Gram per Liter (g/L)

One thousandth of a kilogram per liter. 1 g/L = 0.001 kg/L = 1,000 mg/L. Standard for moderate concentrations in analytical chemistry.

Common use: Laboratory chemical solutions, industrial process solutions, and chemical specifications.

Milligram per Liter (mg/L)

One thousandth of a gram per liter. 1 mg/L = 0.001 g/L = 1 ppm (for dilute aqueous solutions). Standard for trace contaminant measurements.

Most common in: Water quality testing, environmental analysis, drinking water standards, and trace analysis.

Parts Per Million (ppm)

One part solute per million parts of solution. 1 ppm ≈ 1 mg/L for dilute aqueous solutions at standard temperature. Most widely used unit in water chemistry and environmental testing.

Important caveat: For non-aqueous or dense solutions, ppm ≠ mg/L. The relationship depends on solution density.

Grain per Gallon (gr/gal)

Traditional US unit still used in water treatment. 1 gr/gal (US) ≈ 17.1 mg/L. Common in hardness measurements and North American water quality.

Common in: Water hardness (where 1 gpg = 1 grain/gallon), water softening systems, and US water treatment standards.

Pound per Gallon (lb/gal)

North American unit for concentrated solutions. 1 lb/gal (US) ≈ 120 kg/L. Standard for industrial chemical solutions in the US.

Application: Industrial chemical shipments, concentrated acids and bases, and US process specifications.

Pound per Million Gallons (lb/Mgal)

Very dilute concentrations in large water systems. 1 lb/Mgal (US) ≈ 0.12 mg/L. Used for trace contaminants in municipal water treatment.

Application: Large water utility measurements, municipal water standards, and dilute contaminant reporting.

Pound per Cubic Foot (lb/ft³)

Bulk density measurement. 1 lb/ft³ ≈ 16 kg/m³. Used for solids dispersed in liquids and slurry concentrations.

Application: Suspended solids, slurry calculations, and powder dispersions in industrial systems.

Key Relationships & Important Distinctions

• For dilute aqueous solutions: 1 ppm ≈ 1 mg/L (because water density ≈ 1 kg/L)
• For non-aqueous solutions: ppm and mg/L are NOT equivalent; must account for solution density
• Water hardness: Often reported in gpg (grains per gallon) where 1 gpg = 17.1 mg/L as CaCO₃
• For density conversions: mg/L = ppm × solution density (kg/L)
• 1 kg/L = 1,000 g/L = 1,000,000 mg/L
• 1 lb/gal (US) = 8.345404 kg/L
• 1 gr/gal (US) = 0.01714 kg/L ≈ 17.14 mg/L

Typical Solution Concentrations by Application

• Drinking water pH adjustment: 0.01-0.1 g/L chemical
• Swimming pool chlorine: 2-5 mg/L
• Water hardness (soft): <60 mg/L (as CaCO₃)
• Water hardness (hard): >180 mg/L (as CaCO₃)
• Typical tap water dissolved solids: 100-500 mg/L total
• Drinking water limits (EPA): Many contaminants <1-10 mg/L
• Industrial cooling water: 100-1,000 mg/L treatment chemicals
• Pharmaceutical solutions: 0.01-10 g/L active ingredient
• Chemical manufacturing feedstock: 10-100 kg/L (concentrated)
• Stock solutions for dilution: 1-10 kg/L typical
• Environmental contamination: 0.001-10 mg/L typical ranges
• Seawater salt content: ~35 kg/L (3.5% w/v)

Critical: ppm vs mg/L - The Density Factor

Many people assume ppm = mg/L, but this is only true for dilute aqueous solutions where solution density ≈ 1 kg/L (specifically 1.0 kg/L at 4°C).

Correct relationship:

mg/L = ppm × (Solution Density in kg/L)

Examples:

• 100 ppm in water (density 1.0 kg/L) = 100 mg/L ✓
• 100 ppm in concentrated H₂SO₄ (density 1.84 kg/L) = 184 mg/L
• 100 ppm in mineral oil (density 0.87 kg/L) = 87 mg/L

Always verify the solution composition when converting between ppm and mass/volume units!