Question: 1 ppm is equal to how many tds?
Answer: TDS ppm₅₅₀ = 550 ∙ σ, where σ is the conductivity in mS/cm. Sometimes TDS meters display information in ppt, which means “parts per thousand”. Although ppt usually means “parts per trillion”, in TDS meters it means “parts per thousand”. To convert ppm to ppt, divide the value in ppm by 1000 (1000 ppm = 1 ppt).