dKH to PPM & reef salinity converter
Convert common reef values in seconds. Enter a number in either field to update the other.
KH / Alkalinity
Convert carbonate hardness between dKH and ppm (CaCO3).
Reference: 1 dKH = 17.848 ppm (CaCO3).
Salinity
Convert salinity between ppt and specific gravity at 25°C (approx).
Reference: 35 ppt ≈ 1.026 SG at 25°C; temperature affects readings.
How to convert dKH to ppm and back
Use ppm = dKH × 17.848 to convert an alkalinity reading to ppm as calcium carbonate. To convert ppm to dKH, use dKH = ppm ÷ 17.848.
Worked examples
8 dKH to ppm: 8 × 17.848 = 142.784, or 142.8 ppm as CaCO3 when rounded to one decimal place.
150 ppm to dKH: 150 ÷ 17.848 = 8.404…, or 8.4 dKH when rounded to two decimal places.
The calculator rounds ppm to one decimal place and dKH to two, and removes trailing zeros. These examples convert units; they are not dosing instructions.
What does “ppm as CaCO3” mean?
Aquarium alkalinity tests can report the same measurement in dKH or ppm as calcium carbonate (CaCO3). The CaCO3 label expresses alkalinity on a common reference scale. A calcium test's ppm reading measures a different parameter and cannot be converted to dKH with this formula.
Check that your test reports alkalinity in ppm as CaCO3 before using the ppm field. Values reported in meq/L, calcium ppm, or total dissolved solids (TDS) need a different interpretation.
Learn about these reporting units in Hanna Instruments’ guide to saltwater aquarium testing.
| dKH | ppm as CaCO3 |
|---|---|
| 1 | 17.8 |
| 5 | 89.2 |
| 6 | 107.1 |
| 7 | 124.9 |
| 8 | 142.8 |
| 9 | 160.6 |
| 10 | 178.5 |
| 11 | 196.3 |
| 12 | 214.2 |
Understand your reef test results
Once your readings use the same units, compare them with your tank's history and review what affects alkalinity.
Convert units as you log measurements in Reef Buddy
Reef Buddy includes a conversion tool directly where you enter your tank measurements. Convert units while logging your water parameters, and keep your measurements, notes, and dosing plans together.
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