Two-part epoxies have a resin component and a hardener component. A mix ratio indicates the amount of resin and the amount of hardener to be measured, by volume or by weight. Each type of epoxy product requires its own mix ratio, specified by the manufacturer.
An example of a mix ratio is 2:1, which means you need to measure 2 parts resin to 1 part hardener, by volume. Epoxy resin and hardener can also be measured by weight (on a gram scale). For example, a mix ratio of 100A:38B indicates that you need to measure 100 parts of Part A resin to 38 parts of Part B hardener. A third way to automatically measure and dispense epoxy is by using metered epoxy resin and hardener pumps, which are pre-calibrated to dispense the appropriate mix ratio (by volume) of resin and hardener for a particular epoxy product. Using the appropriate pumps, and regardless of the mix ratio, you only need to press down one full stroke on the resin pump and one full stroke on the hardener pump, and the pumps measure the proper mix ratio for you.
Regardless of whether you measure epoxy by volume, by weight, or using metered pumps, the first number in a mix ratio always refers to the resin component, and the second number always refers to the hardener. Before you start measuring, be sure you use the recommended mix ratio (by weight or by volume), as specified on the product label. The cure speed is dictated by the selected hardener, not the amount of hardener. Failure to use the correct mix ratio can result in an improper cure.