Van Herk Margin Calculator

Plan confidently using systematic and random error inputs. Switch between direct totals and component entry. Get margins, exports, and examples in one place fast.

Inputs
All error inputs are assumed to be in millimeters.
White theme • Responsive grid
Choose totals, or compute totals using RSS.
Defaults match the classic formulation.
Controls displayed precision for results and exports.
Represents patient-to-patient variation (systematic).
Represents fraction-to-fraction variation (random).
Component entry (RSS totals)
Totals are computed as root-sum-square: total = sqrt(a² + b² + ...).
Multiplier for Σ term.
Multiplier for σ term.
Optional extra allowance (e.g., policy-based).
Reset

Formula used

The classic Van Herk margin estimate is:

M = 2.5×Σ + 0.7×σ

This calculator also supports custom coefficients and an optional additive term to match local protocols or study assumptions.

How to use this calculator

  1. Select Direct totals or From components.
  2. Enter values in millimeters (use decimals if needed).
  3. Choose the default coefficients or set custom coefficients.
  4. Optionally include an additional margin term.
  5. Press Calculate margin to view results above the form.
  6. Use Download CSV or Download PDF to save results for documentation.

Note: This tool is for educational and documentation support. Always follow your clinical QA and institutional guidelines.

Example data table

Case Σ (mm) σ (mm) Margin (mm)
A 1.5 1.0 4.45
B 2.0 1.5 6.05
C 1.0 0.5 2.85

Example margins use the default coefficients (2.5, 0.7) with no additive term.

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Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.