Mass Accuracy Calculator Formula

Understand the math behind the mass accuracy calculator. Each variable explained with a worked example.

Use the Mass Accuracy Calculator

Formulas Used

Mass Error (ppm)

error_ppm = (measured_mass - theoretical_mass) / theoretical_mass * 1e6

Mass Error (mDa)

error_mda = abs(measured_mass - theoretical_mass) * 1000

Variables

VariableDescriptionDefault
measured_massMeasured m/z180.0637
theoretical_massTheoretical m/z180.0634

How It Works

Mass Accuracy in Mass Spectrometry

Mass accuracy is the difference between the measured and theoretical mass of an ion, expressed in parts per million (ppm). It determines how confidently you can assign a molecular formula.

Formula

Error (ppm) = (m_measured - m_theoretical) / m_theoretical × 10⁶

Modern high-resolution instruments achieve < 2 ppm (Orbitrap) or < 1 ppm (FT-ICR). Time-of-flight (TOF) instruments typically achieve 2-5 ppm.

Worked Example

Glucose [M+H]+ measured at 180.0637, theoretical 180.0634.

measured_mass = 180.0637theoretical_mass = 180.0634
  1. 01Error = (180.0637 - 180.0634) / 180.0634 × 10⁶
  2. 02Error = 0.0003 / 180.0634 × 10⁶ = 1.67 ppm
  3. 03Error in mDa = 0.3 mDa

Ready to run the numbers?

Open Mass Accuracy Calculator