Linear x-axis with a 4-decade logarithmic y-axis: the standard sheet for plotting exponentials and decay curves.

Free semi-log graph paper PDF. Linear horizontal axis, 4-decade logarithmic vertical axis for plotting exponential growth, decay and dose-response data.

Semi-Log Graph Paper | Free Printable PDF (4 Decade)

Semi-Log Graph Paper

If your data starts at 0.03, label the bottom decade '0.01' so the value lands in the third subdivision up. If it starts at 30, label it '10'. The decades themselves are unitless; you anchor them when you label.

Pick the bottom decade to match your smallest value

A straight line covering one full decade in 5 cm tells you the quantity multiplies by 10 every 5 cm of x. Convert by dividing: k = ln(10) / (x-span per decade). For exponential decay, this is also how you read off the half-life from the line.

Read the slope as a multiplicative rate

If the data doesn't form a straight line, the process isn't a pure exponential. Concavity tells you whether it's slowing down (saturation) or speeding up (autocatalysis). That diagnostic is the main reason to plot data on semi-log even before you fit a model.

Curves on semi-log mean it's not exponential

log(0) is undefined and log(-1) is imaginary. Either drop those points or shift the data by a known offset before plotting. Don't pretend a 0 is a 0.01; that's a tell that hides real noise.