One of the big questions people always ask when working with epoxy resin is “How much resin do I need?”. This is especially important with epoxy resin because you have to mix up what you need for a project and then have a fixed working time to use what you’ve mixed. Which means if you mix too much and don’t have another project prepared, that resin will harden and be wasted. Even worse is when you’re partway through a project and run out of mixed resin. This is especially problematic if you are combining colors or swirling colors together. The resin needs to be a viscous liquid for this to work, so waiting on a new batch of resin can be impossible and ruin a project. Now using our simple Epoxy Calculator on the projects you're going to work on and take some basic measurements!
Fortunately, there are useful tools to help you avoid miscalculating the amount of resin you will need for a project. Not surprisingly the first tool is an Epoxy Calculator. The epoxy calculator is pretty straightforward. Use a ruler to measure the mold or tray you’ll be filling with resin. Plug those measurements into the calculator and up pops the total amount of resin you need for that object. It’s very important to remember that the volume measurement you get is the TOTAL volume of the resin plus the hardener (Part A + Part B). So, before you measure out your resin, divide that volume in half, and that new number is the amount you need of the resin and the amount you need of hardener.
For example: If I have a mold that’s 1 inch long, 2 inches wide, and a half inch thick (or deep), I plug those measurements into the Epoxy Calculator, and the Epoxy Calculator will tell me I’ll need a total of .54 ounces of mixed resin. That means I’ll need .27 ounces of hardener plus .27 ounces of resin.
The very best way to accurately measure equal parts of resin and hardener, is to use a kitchen or postal scale. I line my scale with wax paper and pour the resin and the hardener in one cup. Then I start mixing immediately.
It’s important to note that different shapes may have the same measurements, but different volumes. An oval that measures 1 inch long, 2 inches wide, and a half inch thick, will need less resin than a rectangle that also measures 1 inch long, 2 inches wide, and a half inch thick. For small objects like pendant molds, I wouldn’t worry about the difference because I’d recommend mixing a little extra resin anyway, and the leftover amount will be very small.
However, for larger oval and round molds, or molds that have a very irregular shape, you may need to try another method of figuring out the volume of resin you’ll need. One excellent method is using water as a placeholder for the resin. For this method you will need the mold you want to measure, a measuring cup that you can mix resin in, and water. You may prefer a scale to a measuring cup, but more on that in a minute.
First fill your mold with water to the very top. Then pour that water into the measuring cup. Now read the volume of water in the measuring cup and you know the total amount of resin you need. That’s it. Again, remember that before you measure out your resin, you have to divide that volume in half, and that the new number is the amount you need of the resin and the amount you need of hardener.
Important: If you are going to use your mold or measuring cup for resin right away, make sure that they are totally dry first!
Now, back to the scale. If you want to figure out how much resin you need by weight, not volume, you’ll need a precise kitchen or postal scale. Pour the water from the mold into any container (don’t add in the container weight) and weigh the water. The catch is that resin is denser than water by about 8%. So when you weigh the water from your mold, add another 8%. If you want your calculations to be easier, just round up and add 10%.
I’ll just add one more piece of advice about determining your project’s resin requirements: Whatever measurement you get, add a little extra. Especially as the resin starts to thicken, it sticks to the inside of your measuring cup, and to the stirring sticks. If you’re dividing the mixed batch into portions to make different colors, you’ll lose a little more resin in this process also.
And then there are drips. You don’t want to measure so precisely that you can’t afford a few drips.
So the important takeaway here is to calculate how much resin you need as accurately as you can and then add a little extra to the total weight or volume. That way you will always have enough resin, but never much too much.
You are now armed with three great tools to help you figure out how much resin you need to purchase and mix for your projects. The Epoxy Calculator is certainly the easiest, and will work in most circumstances, from jewelry molds to resin tables. And when a shape is too irregular to calculate, like a figurine or a sphere, you can use the water volume method to figure out either the volume or the weight of the resin you’ll need. One of these techniques should work for the vast majority of your epoxy resin projects.