Volume to Area Liquid Calculator

A volume to area liquid calculator finds how much liquid covers each unit of surface area. It divides a volume of liquid, usually measured in gallons, by the surface area that liquid must cover, usually measured in square feet. The result is a coverage ratio in gallons per square foot. It works for paint, wood stain, concrete sealer, epoxy floor coating, liquid fertilizer, and waterproofing compounds.

How to calculate gallons per square foot

The formula is:

$\text{Gallons per Square Foot} = \frac{\text{Volume (Gallons)}}{\text{Area (Square Feet)}}$

Divide the amount of liquid available by the surface it will cover. The result shows how much liquid falls on each square foot of surface. If the area entered is zero, the calculator returns zero instead of an error.

Variables

• Volume (gallons): the amount of liquid, in US gallons. One US gallon equals about 3.785 liters, or 231 cubic inches.
• Area (square feet): the surface to be covered, in square feet. One square foot equals about 0.093 square meters, or 144 square inches.
• Gallons per square foot: the coverage ratio the calculator returns, shown to four decimal places. Four decimal places matter here because thin coatings, such as sealers, often need rates below 0.01 gallons per square foot, where small differences change how thick the coat ends up.

Example calculation

A deck measures 200 square feet. It needs sealing, and 5 gallons of sealer are on hand.

Gallons per square foot = 5 ÷ 200 = 0.0250

Most deck sealers call for 0.0050 to 0.0100 gallons per square foot. At 0.0250, this is 2.5 to 5 times more sealer than the surface needs. At a middle rate of 0.0075 gallons per square foot, the same deck would only need 200 × 0.0075 = 1.5 gallons.

Converting coverage units

Paint cans sold in the United States often list coverage as square feet per gallon rather than gallons per square foot. The two figures are reciprocals of each other. Paint that covers 400 square feet per gallon uses 1 ÷ 400 = 0.0025 gallons per square foot.

Metric labels usually state coverage in liters per square meter. One gallon per square foot equals about 40.75 liters per square meter.

Typical coverage rates

Coverage needed depends on the product and the surface. These ranges are general starting points. The manufacturer's label always takes priority over any general figure.

A porous surface, such as raw wood or bare drywall, absorbs more liquid than a sealed surface. A first coat on a porous surface often needs 20 to 30 percent more liquid than the label suggests, because the coat both covers the surface and fills its pores. Spray application also uses more liquid than a brush or roller. Overspray, liquid that never reaches the surface, commonly wastes 20 to 30 percent of the total.

How to use the calculator

1. Enter the volume of liquid on hand, in gallons. Decimals are allowed.
2. Enter the area to be covered, in square feet. Decimals are allowed.
3. Read the coverage ratio, shown in gallons per square foot.
4. Compare the ratio to the coverage rate printed on the product label or data sheet.
5. Add extra for waste. A common allowance is 5 to 10 percent for brush or roller work, and 20 to 30 percent for spray work.

Frequently asked questions

What is the formula for gallons per square foot?

Gallons per square foot equals the volume of liquid, in gallons, divided by the area it covers, in square feet.

How many gallons of paint are needed for a room?

Divide the wall area by the coverage rate printed on the paint can. For 1,200 square feet of wall at a rate of 400 square feet per gallon, that is 1,200 ÷ 400 = 3 gallons.

How is square feet per gallon converted to gallons per square foot?

Divide 1 by the square-feet-per-gallon figure. A paint that covers 400 square feet per gallon equals 1 ÷ 400 = 0.0025 gallons per square foot.

Does this calculator work for products other than paint?

Yes. Any liquid applied over a surface can be measured this way, including wood stain, concrete sealer, epoxy coating, liquid fertilizer, and waterproofing compounds, as long as the volume is entered in gallons and the area in square feet.

Why does a small change in the ratio matter?

Thin coatings often need rates under 0.01 gallons per square foot. A shift from 0.0025 to 0.0033 gallons per square foot, for example, is a real difference in how thick the finished coat will be, even though the numbers look close.

Does surface porosity change the math?

The division itself does not change. A porous surface simply absorbs more liquid than a sealed one, so the actual amount used on a raw or unsealed surface is often higher than the calculated ratio alone would suggest.

Related calculators

• Area calculator, for surfaces that are not simple rectangles
• Unit converter, for gallons, liters, square feet, and square meters
• Paint calculator, for room-specific paint estimates
• Volume calculator, for the volume of liquid in a container