Limit of Detection Calculator
The limit of detection and limit of quantification of an analytical method from the scatter of blank readings and the slope of the calibration curve.
A signal is only distinguishable from nothing once it clears the noise: the ICH convention sets the limit of detection at 3.
How the limit of detection calculator works
A signal is only distinguishable from nothing once it clears the noise: the ICH convention sets the limit of detection at 3.3 times the standard deviation of the blank divided by the calibration slope, and the limit of quantification — where the result is precise enough to report a number — at 10 times. Paste your blank readings (or enter their standard deviation directly) and the slope from your calibration.
Formula: LOD = 3.3 σ ÷ m; LOQ = 10 σ ÷ m
Worked examples
| Inputs | Limit of detection | Note |
|---|---|---|
| Seven blanks, slope 0.1 | 0.00795 | LOD ≈ 0.0079 |
| σ entered directly | 0.0099 | LOD 0.0099, LOQ 0.03 |
| A noisier method | 0.66 | LOD 0.66 |
FAQFrequently asked questions
Why 3.3 and 10?
The ICH Q2 guideline: 3.3σ gives about a 5% chance of a false positive and a 5% chance of missing a real signal at the LOD; 10σ corresponds to a relative standard deviation of about 10%, the usual threshold for reporting a number.
Blank readings or the standard deviation of the intercept?
Either is accepted. Replicate blanks (or a very low standard) are the most common; the residual standard deviation of the calibration line or the standard deviation of the intercept are the alternatives ICH lists.
How many blanks?
At least seven to ten for a meaningful standard deviation; three is the bare minimum the calculator accepts and gives a rough figure.
Is a result below the LOQ reportable?
As "detected, below the limit of quantification" — you can say it is there but not how much. Below the LOD it is "not detected".
Where these figures come from
- IUPAC — Standard atomic weights (2021 conventional values) — the molar-mass table
- NIST — CODATA 2018 fundamental physical constants — Avogadro constant, gas constant, speed of light
- NIST Chemistry WebBook — thermochemical data
- CSIRO — Australia's national science agency
Last checked: September 2026. Atomic masses are the IUPAC conventional values; constants are CODATA 2018; equations are the standard textbook forms.