In large part because of my orientation to baking, I have come to prefer the use of mass units to volume units. Mass provides a consistent quantity regardless in variations in state of the ingredient or measurement technique. Flours are particularly variable in volume measurement, but a lot of ingredients are more straightforward to measure using mass. Simply tare the scale for each ingredient added.
Although Canadians are quite used to recipes using American measurements, Canada is on the metric system and newer recipes use metric measures. For this reason, and because of the increased precision, my recipes usually use grams instead of ounces. Some recipes converted from American measures have an obvious conversion factor applied. Some small measures, such as for salt and extracts, are not fully accurate at just the gram level of precision, and volume measures are sometimes preferred for these.
Normally, exact conversion between measures is not critical. It is convenient to develop recipes in reasonably round units of the chosen measurement system. Therefore, an ounce may become 25 grams instead of 27 grams, a pound 450 grams instead of 454 grams. Some recipes may stray further than others for round measures, depending on importance.
For convenience, many of my recipes include both mass and volume measures--normally mass first in newer recipes. Because rounding of measures is designed to be suitable to the recipe as a whole, the conversion is sometimes highly inexact. Therefore it is best to use either the mass or the volume measures; using either for different ingredients may have unpredictable results.
Below is a table of conversions between measures. The conversions are only mass-to-mass or volume-to-volume, because these do not vary by ingredient. Mass-to-volume conversions for specific ingredients is sometimes included with the ingredient description.