Limit of Detection Calculator
LOD and LOQ from blank noise and calibration slope.
Work out Limit of Detection. LOD and LOQ from blank noise and calibration slope. Shows every step's contribution, not just the total.
From repeated measurements of a blank, or the residual standard deviation of the calibration line.
Signal per unit concentration, from your standard curve.
Limit of detection
0.066
Limit of quantitation 0.2 — 3.03× higher
LOD = 3.3σ/S and LOQ = 10σ/S, following ICH Q2(R1). The multipliers are conventions rather than physics: 3.3 gives roughly 95% confidence that a signal is real rather than noise, and 10 gives about 10% relative standard deviation, which is the usual floor for reporting an actual number. Between the two limits the honest report is "detected but not quantifiable", not a number with wide error bars. Below the LOD it is "not detected", which is not the same as "zero". Both figures come out in the same units as your calibration concentrations, and both depend on the instrument and the day. They should be re-established with the method, not quoted from a previous run.
How the Limit of Detection Calculator works
Enter the standard deviation of your blank and the slope of your calibration line to get both limits by the ICH definitions. Between them the honest report is that something was detected but cannot be quantified — which is not the same as a number with wide error bars.
Also known as: lod loq calculator · detection limit calculator · limit of quantitation calculator · 3.3 sigma over slope
Frequently asked questions
How do I calculate limit of detection?
LOD = 3.3σ/S, where σ is the standard deviation of the blank and S is the calibration slope. LOQ uses 10 in place of 3.3.
Where do 3.3 and 10 come from?
They are conventions from ICH Q2(R1), not physical constants. 3.3 gives roughly 95% confidence that a signal is real rather than noise; 10 gives about 10% relative standard deviation, the usual floor for reporting a number.
What is the difference between LOD and LOQ?
LOD is the smallest amount you can reliably say is present. LOQ is the smallest you can put a number on. Between them you report 'detected, below quantitation limit'.
Does 'not detected' mean zero?
No, and reporting it as zero is wrong. It means below the detection limit of that method on that day, which is why the LOD should be quoted alongside any non-detect result.
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