I can’t tell you how many times I’ve gotten to the end of my pour and found that I either have way too much paint or not nearly enough. As a beginner, this was very frustrating, and I wished I had an easier way to help me gauge how much paint I needed.
So how much paint do you need for an acrylic pour? In general, it takes approximately 1 ounce of paint per 25 square inches of surface area. In metric measurements, this would be just over 1 milliliter per square millimeter. “Surface area” should include any area that will be painted, which usually includes the sides of the object, which most people forget.
This calculation can vary slightly depending on the size and shape of the object you are painting, the surface roughness, the consistency of the paint, and the painting materials being used. In this blog post, you’ll learn about how these considerations impact that amount of paint you’ll need. Understanding these concepts should allow you to better estimate your paint requirements in the future.
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Measuring the Size and Shape of the Painting Surface
Before you start a paint pouring project, it is important to understand where you want your paint to end up. This first step to doing this is to review the surface you plan on painting.
Use a ruler or measuring tape to calculate the area you are looking to cover with paint. Measure every surface that you expect to be painted including the top and sides of the piece. If an area is not regular in shape, decide which type of shape it most resembles and calculate the surface area from there.
Use the following information for common surface area calculations.
- Rectangle = Base × Height
- Square = Base × Height
- Triangle = ½(Base × Height)
- Parallelogram = Base × Height
- Trapezoid = ½(Base1 + Base2) × Height
- Circle = π(radius)2 = πr2
By measuring the entire painting surface before mixing any of your paints and using the chart above to better estimate your needs, you’ll find that you don’t miscalculate the amount of paint you need nearly as often.
Surface area is by far the most important factor in determining paint needs, but it is definitely not the only consideration. Continue reading to learn some of the other common reasons painters might experience paint estimation issues.
Why Surface Roughness Matters
Imagine pouring a cup of paint on a kitchen table. Now imagine pouring the same amount of paint on the carpet in your living room. In this example, the paint will spread out on the kitchen table on a much wider area than it will on the carpet floor.
Why does this happen? Think about the actual surfaces that the paint is coming in contact with. The kitchen table is smooth and there is nothing that keepsthe paint from moving around.
With the carpet, the paint has to go over and around the roughness of the carpet as it settles. That means there is more surface area that the paint ultimately has to cover per square in of carpet.
While carpet is a little more extreme example of this phenomenon, it is important to note that even doing an acrylic pour on the roughness of a brand new canvas can increase the amount of paint needed for coverage when compared to doing the same paint pour on a gessoed or prepared canvas.
Of the common materials used in pour acrylic painting, wood art panels and other well-sanded and prepared surfaces will take the least amount of paint. Rough cut wood sections and other unfinished wood products will usually require the most paint. Stretched canvases sit somewhere in the middle.
Another consideration to take into account when planning how much paint to use for a pouring project is the consistency of paint. In general, the thicker the paint is, the more it will take to cover a similar area when compared to a thinner paint.
Lets take a look at why this happens. To illustrate, imagine pouring a cup of honey and a cup of water out at the same time. Which cup will empty faster? The water will, of course. There might be the same amount of each, but they are not behaving in the same way.
Without going into too much chemical theory, this is a property of the viscosity of liquid. The thicker a liquid, the less room the molecules in the liquid have to move around each other.
Those “fat” molecules also don’t move around each other very well. Because of this, those molecules are said to have a higher friction level. Thinner liquids, like water, have very low friction levels so they flow and move much more readily.
In addition, the more room the molecules have, the fast they will move around. Increased movement in molecules provides greater viscosity, and thus improves how the paint flows. Changing the state of the liquid by pressurizing it or adding heat can also increase viscosity. I do not recommend pressurizing your paint.
Now that you understand how viscosity works, how does that affect how much paint you’ll be using on an acrylic pour? Thicker paints will tend to stay thicker when sitting on a surface. This is because the paint is less likely to “move” unless some other force acts on the paint.
You can easily test this theory by using the same example of the honey and the water. Once the honey and water are poured on the table, which makes the bigger puddle? The water does. The honey will always create a thicker layer than the water.
Covering a canvas with a thicker consistency paint will always require more than doing so with a thinner paint because of these factors. A coat of paint that is too thick can cause crazing and cracking. Thin paint will cover a canvas more easily; however, it can also leave too little paint on some parts of the surface, causing the colors to be muddled or showing the underlying surface through the paint.
The last contributing factor to estimating the amount of paint you’ll need for an acrylic pour is the materials that are used in your paint mixture.
Every paint is not created equal. Some paints are plant based, some are chemical based, and some are even metal based. Each one has it’s own unique properties and behaviors.
Metal paints tend to be heavier. This causes the paint to be affected by gravity a little more than other more lightweight paints. Heavier paints generally have higher friction levels and, therefore, don’t move a rapidly as other types of paints. Heavy paints are also made up of bulkier molecules compared to many other paints, which contributes to the paint being more viscous than other paint.
The opposite is true of some chemical and plant based paints. Their “weight” is much less compared to most metal based paints, and their molecular structure is less dense. As you learned before, this makes the viscosity of the paint less. Less viscous paint will flow better and move more readily on a painting surface.
Each paint is unique. Some more expensive paints will show the relative weight of the paint on the container. With less expensive paint, you will need to do some testing on your own to get a feel for the different properties of the different colors.
If it wasn’t apparent already, you should now realize that gauging the amount of paint needed for an acrylic pour project is not an exact science. Surface area, the roughness of the painting surface, viscosity, and the materials used in the paint all have an impact on how the paint flows and how well it covers the canvas.
Start your base paint needs calculation with 1 ounce of paint per 25 square inches of surface area. Then adjust for contributing factors mentioned in this article, and you should be able to better gauge your paint needs. With additional practice, you will be able to do this without thinking.
Why don’t I use the same amount of paint every time? Every painting is different. The number of paints used, the consistency of each, the air temperature and humidity, how much you tilt, the thickness of the paint left on the canvas, and many more factors all contribute to the amount of paint used during a pour.
What if i don’t have enough paint? If you don’t have enough paint to cover your canvas, just add more. Some of my favorite pieces have come from adding more paint to my project when I underestimated the amount of paint that I needed. Try adding a new color or mix them slightly differently to give some variation to your piece.