ppm ↔ mg/L Converter

Lab and permit reports mix ppm, mg/L, ppb and µg/L for the same contaminant, and a misplaced assumption about what they mean is the quiet source of out-of-spec readings. For dilute aqueous solutions the relations are exact and simple, so this converter does them with no guesswork and states the one condition that makes them true.

Convert ppm ↔ mg/l units

Value

From

Why ppm and mg/L get confused

In water quality both ppm (parts per million) and mg/L describe the same dilute concentration, because a litre of water at about 4 °C weighs one kilogram. So 1 ppm by mass equals 1 mg/L, 1 mg/kg and 1 g/m³, and 1 ppb equals 1 µg/L. The converter applies exactly these equalities.

The catch is the word aqueous. The 1:1 ppm-to-mg/L equivalence holds for dilute water-based samples; for oils, sludges or concentrated process streams you must convert through the actual density or mass fraction, not this tool. Keep that condition in mind and the numbers are exact.

Where each unit appears

Regulations and discharge permits in many markets write limits in mg/L, while older or North American reports use ppm and ppb. Instrument displays and lab certificates quote µg/L for trace metals and ppb for low-level organics. g/m³ is the same as mg/L and shows up in gas-absorption contexts; mg/kg is the solid-sample equivalent.

Complete conversion reference

Convert 1 unit to	ppm	ppb	mg/L	µg/L	mg/kg	g/m³
1 ppm	1	1000	1	1000	1	1
1 ppb	0.001	1	0.001	1	0.001	0.001
1 mg/L	1	1000	1	1000	1	1
1 µg/L	0.001	1	0.001	1	0.001	0.001
1 mg/kg	1	1000	1	1000	1	1
1 g/m³	1	1000	1	1000	1	1

Instruments for this measurement

CON100

3-in-1 pen: conductivity, TDS, salinity

Pocket · field inspection

CON200

Handheld conductivity / TDS / salinity tester

To 400 mS/cm · IP65

CON600

Benchtop conductivity / TDS / salinity meter

0.001 µS/cm resolution

Process Measurement

Flow, pressure, level & temperature

Electromagnetic / vortex / TX

All 195+ Products

Full instrument catalogue

Filter by application

Models shown are representative families, not a complete catalogue. Send us your application, water analysis and installation constraints and we will match instruments to it.

Frequently asked

Is 1 ppm equal to 1 mg/L?

For dilute aqueous solutions, yes — 1 ppm (w/w) = 1 mg/L = 1 mg/kg = 1 g/m³. This equivalence assumes the sample is mostly water at roughly 1 kg/L, which is true for the dilute waters these units describe. It does not hold for oils or concentrated streams.

What is the difference between ppm and ppb?

ppb is one thousandth of ppm: 1 ppm = 1000 ppb, just as 1 mg/L = 1000 µg/L. Trace-metal and low-level limits are usually written in ppb or µg/L, while main parameters use ppm or mg/L.

Why do permits use mg/L but meters show ppm?

Both express the same dilute-water concentration; the choice is regional and historical. Convert with this tool rather than treating them as different measurements, and keep the aqueous-sample condition in view.

When is ppm NOT the same as mg/L?

When the matrix is not dilute water — oils, sludges, high-solids or concentrated chemical streams. There the mass-per-volume (mg/L) and mass-fraction (ppm) values diverge with density, so use the actual density or a direct mass-fraction measurement instead.

This page performs exact unit arithmetic with no physical assumption beyond the stated reference (for example mH₂O assumes water near 4 °C, and pH follows its logarithmic definition). It is a working aid, not a substitute for the measurement method named in your permit.