How this calculator works
Use a previously established straight-line calibration in the same units as the sample measurement. The intercept represents the blank or background; the slope converts concentration to signal. Negative slopes and backgrounds are permitted, but inferred concentrations must be nonnegative. This page evaluates coefficients you supply; it does not fit standards or estimate measurement uncertainty. A line drawn beyond measured standards is an extrapolation.
Formula
y = a x + b; x = (y - b)/a; a = (y - b)/x; b = y - a x.
Worked example
For a sensitivity of 2 and background of 1, a signal of 7 corresponds to concentration 3. A concentration of 4 with sensitivity 3 and background -2 gives signal 10.
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Frequently asked questions
Which concentration units should I use?
Use the units used to determine your sensitivity, such as mg/L or micromol/L.
Can the slope be zero?
A flat response can predict signal, but it cannot identify a concentration.
Does a line prove assay validity?
No. Check the standards, residuals, working range and matrix effects for your assay.