Log-log graph paper, A4
Both axes logarithmic on A4, four decades, for power laws and anything spanning orders of magnitude.
Opens with these settings already loaded. Change anything you like, then download as PDF, PNG or SVG.
Log-log straightens power laws, semi-log straightens exponentials
This is the distinction that decides which sheet you want. A relationship of the form y equals a times x to the power n plots as a straight line on log-log paper, and the slope of that line gives you the exponent directly. A relationship of the form y equals a times b to the power x straightens on semi-log instead. Plotting on the wrong one gives you a curve and no easy way to read the parameter you were after.
Reading the slope is the point
On log-log paper the slope of a straight line is the exponent n, measured as the ratio of decades risen to decades run rather than in ordinary units. A line climbing two decades while moving one has a slope of 2, meaning y varies with x squared. This is why log-log is a diagnostic tool and not just a way to fit big numbers on a page: the shape of the plot tells you the form of the relationship.
Count your decades before you print
Each decade is one factor of ten, and you cannot extend a logarithmic axis by taping on another sheet the way you can a linear one. Work out the range your data spans in both directions, then choose at least that many decades. Four covers a range of ten thousand to one, which handles most laboratory and engineering data. Too many and your points crowd into a corner.
Printing it accurately
This only measures correctly if your printer doesn't rescale the page. In the print dialog set Scale: 100%, not "Fit to page" or "Shrink oversized pages". If you're not sure it worked, print the calibration page, measure the ruler on it with a real ruler, and it will tell you exactly what your printer is doing to the page.