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📏 LOD / LOQ Calculator

Calculate Limit of Detection (LOD) and Limit of Quantification (LOQ) using the calibration-curve method.

Standard Deviation (σ) of blank response or regression residual

Slope (S) of calibration curve

Limit of Detection (LOD)

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Limit of Quantification (LOQ)

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💡 Note: σ can come from the standard deviation of repeated blank measurements, or from the standard deviation of the residuals (y-intercept) of your calibration curve — check which your protocol requires (both are accepted approaches per ICH Q2(R1)).

📖 Example: σ = 120 (signal units), S = 2500 (signal per µg/mL): LOD = 3.3 × 120 / 2500 = 0.158 µg/mL; LOQ = 10 × 120 / 2500 = 0.48 µg/mL.

Frequently asked questions

What's the difference between LOD and LOQ?

LOD (limit of detection) is the lowest concentration that can be reliably distinguished from background noise, but not necessarily measured precisely. LOQ (limit of quantification) is the lowest concentration that can be measured with acceptable precision and accuracy — it's always higher than LOD, typically by a factor of 3 (10σ/S vs 3.3σ/S).

Where do the constants 3.3 and 10 come from?

They come from ICH Q2(R1) guidance, derived from the standard normal distribution: 3.3 corresponds to a signal roughly 3 times the noise (99% confidence of detection), and 10 corresponds to a signal-to-noise ratio that gives acceptable quantitative precision.

Can I calculate LOD/LOQ without a calibration curve?

This calculator uses the calibration-curve-based approach (3.3σ/S and 10σ/S), one of several methods in ICH Q2(R1). Other approaches include visual evaluation of signal-to-noise ratio directly from chromatograms, which don't require this formula.

Accuracy & how this is derived

Derivation: ICH Q2(R1) calibration-curve-based method: LOD = 3.3 sigma / S and LOQ = 10 sigma / S, where sigma is the standard deviation of the blank response (or regression residual) and S is the calibration curve slope.

Validated against: Method specified in ICH Q2(R1) Validation of Analytical Procedures: Text and Methodology, the internationally recognized analytical validation guideline.

⚠️ For educational and research support only — verify critical results independently before use in regulated, clinical, or publication-bound work.

✔ Last updated: July 2026 · Report an error

LOD and LOQ in analytical method validation

Limit of detection and limit of quantification are core figures of merit in analytical method validation, required by regulatory guidelines such as ICH Q2(R1) for any quantitative analytical procedure. The calibration-curve-based approach estimates both from the standard deviation of the response (from blank measurements or regression residuals) divided by the slope of the calibration line, scaled by factors of 3.3 and 10 respectively to reflect statistically meaningful detection and quantification thresholds.