\text{ppt}

part per trillion

Concentration Dimensionlessexact by definition

A part per trillion is 10⁻¹⁰ percent, one part in 10¹². It is the reporting level for the most potent trace contaminants: dioxins, PCBs and PFAS in drinking water are regulated at single-digit ppt, which is roughly one drop in twenty Olympic swimming pools.

Watch out: "ppt" is genuinely ambiguous and this catalog reads it as parts per TRILLION, the dominant meaning in environmental chemistry. Some European and older sources use ppt for parts per thousand, a factor of 10⁹ apart. If a number written ppt is near 35, it is salinity and it means thousand.

1 $\text{ppt}$ (Concentration)	1.0000000e-10 $\text{\%}$
1 $\text{ppt}$ (Dimensionless)	1.0000000e-12 $\text{—}$

As a unit of dimensionless

One part per trillion is exactly 1e-12 of the whole, at the edge of what routine analytical chemistry can measure. Per- and polyfluoroalkyl substances in drinking water are regulated here, with US limits for PFOA and PFOS set at 4 ppt. The factor is exact by definition.

One part per trillion in every concentration unit

1	part per trillion (ppt)this unit
1	nanogram per liter (ng/L)
0.001	parts per billion (ppb)
0.001	microgram per liter (μg/L)
0.000001	parts per million (ppm)
0.000001	part per million by volume (ppmv)
0.000001	milligram per kilogram (mg/kg)
0.000001	milligram per liter (mg/L)
5.84180e-08	grain per US gallon (as CaCO₃) (gpg)
1.00000e-09	part per thousand (ppth)
1.00000e-09	gram per liter (g/L)
1.00000e-10	percent (%)
1.00000e-10	percent by weight (% w/w)
1.00000e-10	percent by volume (% v/v)
1.00000e-10	percent weight per volume (% w/v)
1.00000e-12	fraction (0–1) (fraction)

One part per trillion in every dimensionless unit

1	part per trillion (ppt)this unit
0.001	part per billion (ppb)
0.000001	part per million (ppm)
1.00000e-07	per cent mille (pcm)
1.00000e-08	basis point (bp)
1.00000e-09	per mille (per mille)
1.00000e-10	percent (%)
1.00000e-12	ratio (—)

Solvers that use concentration

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