Mass Accuracy Calculator: ppm Error and Extraction Window

Check measured against theoretical m/z, and set an extraction window.

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Theoretical m/z

Measured m/z

Tolerance ppm

Example: [M+H]⁺ of paracetamol.

Error–

Window low–

Window high–

ppm = (m_measured − m_theoretical)/m_theoretical·10⁶ · window = m_theoretical·(1 ± tol·10⁻⁶)

How it works

Mass accuracy in parts per million normalises the error to the mass, so the same instrument performance can be compared across the mass range. Many high-resolution workflows accept ±5 ppm for formula confirmation, with tighter limits on recently calibrated Orbitrap and Q-TOF instruments.

Below about m/z 200, a fixed error in mDa can look large in ppm, so some laboratories set an absolute mDa limit for small ions.