Gallons per Square Foot Calculator

Gallons per Square Foot Calculator converts square feet to gallons using area and depth. One square foot at 1 inch deep holds 0.623 gallons. At 1 foot deep it holds 7.48 gallons

Gallons per Square Foot Calculator converts square feet to gallons using area and depth. One square foot at 1 inch deep holds 0.623 US gallons. At 1 foot deep it holds 7.48 gallons. Enter your area and depth to get total gallons, coverage per gallon, and pails needed.

Gallons per Square Foot Calculator Formula

Square feet measure area. Gallons measure volume. You cannot turn one into the other without a depth.

Once you have a depth, the math is short. A US liquid gallon is exactly 231 cubic inches, as defined in NIST Handbook 44. One square foot is 144 square inches.

The rate per square foot comes first.

$$G_{sqft}=\frac{D_{in}\times 144}{231}$$

Here, G_sqft is gallons per square foot and D_in is the depth in inches. At 1 inch deep, the result is 144 ÷ 231 = 0.623 gallons per square foot.

Total gallons come from the area.

$$G_{total}=A_{sqft}\times G_{sqft}$$

A_sqft is the area in square feet. In rectangle mode the calculator finds it as length × width.

Coverage is the inverse of the rate.

$$C_{sqft/gal}=\frac{1}{G_{sqft}}$$

C is the area one gallon covers at your depth. The Coverage Rate card shows this value.

If your depth is in feet, there is a shortcut. One cubic foot holds 7.48 gallons.

$$G_{total}=A_{sqft}\times D_{ft}\times 7.48$$

Both methods give the same answer. The calculator uses the inch version, so thin coatings and deep water go in the same field.

Metric mode is simpler. One square meter at 1 mm deep holds exactly 1 liter. Liters per square meter equals the depth in millimeters.

Square Feet to Gallons Chart

Find your depth in the left column. Multiply the second column by your square footage to get total gallons.

All values use US liquid gallons.

Gallons to Square Feet

This is the reverse question. You have a fixed number of gallons and want to know how far they go.

Read the Coverage Rate card. It shows square feet per gallon at your depth. Multiply that number by the gallons you have.

Example: you have 5 gallons of self-leveler to pour at 1/4 inch. Enter 0.25 in the depth field. The Coverage Rate card shows 6.42 sq ft per gallon. The 5-Gal Pail Coverage row shows 32.08 sq ft. That is all one pail covers at that thickness.

Water Example: Lawn or Pool

Water questions usually use whole inches or feet of depth.

One inch of water on a 1,000 sq ft lawn. Choose Known Total Area. Enter 1,000 sq ft and a depth of 1 inch. The result is 623.38 gallons. This is why irrigation guides use 0.62 gallons per square foot per inch of water.

A 12 ft × 16 ft pool filled 4 ft deep. Enter 12 and 16 for length and width. Enter 48 inches for depth. The area is 192 sq ft. The result is about 5,745 gallons. The Equivalent Volume card shows the same water as 768 cubic feet.

The depth must be the same across the whole area. For a pool with a shallow end and a deep end, use the average depth.

Coating Example: Epoxy Floor

A 22 ft × 24 ft garage floor is 528 sq ft. The topcoat spec calls for 15 mils wet film thickness. Fifteen mils is 0.015 inches, so enter 0.015 as the depth.

• Rate: (0.015 × 144) ÷ 231 = 0.00935 gallons per sq ft
• Total: 528 × 0.00935 = 4.94 gallons
• Coverage: about 107 sq ft per gallon
• One 5-gallon pail covers about 535 sq ft at this thickness

The Packaging card shows 0.99 exact pails, rounded up to 1 pail. That leaves almost nothing for edges, spills, or touch-ups. Most crews would order a second pail.

Mils vs Inches

Coating data sheets give thickness in mils. The depth field takes inches. One inch is 1,000 mils.

Typing 15 for a 15-mil coat tells the calculator you want 15 inches of material. The answer comes out 1,000 times too large. Divide mils by 1,000 first. So 15 mils becomes 0.015 inches.

After you calculate, check the Wet Film Thickness row. It should match the mils on your spec sheet.

Frequently Asked Questions

How many gallons are in a square foot?

A square foot has no gallons until you give it a depth. At 1 inch deep, one square foot holds 0.623 US gallons. At 1 foot deep, it holds 7.48 gallons. The formula is depth in inches × 144 ÷ 231. For any other depth, multiply 0.623 by the depth in inches. A 3-inch depth gives 3 × 0.623 = 1.87 gallons per square foot.

How do you convert square feet to gallons?

Multiply the area by the depth, then convert the volume to gallons. With depth in inches, the formula is sq ft × depth × 0.623. With depth in feet, it is sq ft × depth × 7.48. Example: 200 sq ft at 2 inches deep is 200 × 2 × 0.623 = 249.4 gallons. In the calculator, choose Known Total Area, enter 200 sq ft and 2 inches, and read Total Gallons Needed.

How many gallons of water are in a square foot?

One square foot of water 1 inch deep is 0.623 gallons. That water weighs about 5.2 pounds, since a gallon of water weighs about 8.34 pounds. At 1 foot deep it is 7.48 gallons and about 62.4 pounds. The gallon figure is the same for any liquid. Only the weight changes.

How do you convert gallons to square feet?

Divide the gallons by the gallons-per-square-foot rate for your depth. The formula is sq ft = gallons ÷ (depth in inches × 0.623). Example: 20 gallons spread 1/2 inch deep covers 20 ÷ 0.3117 = 64.2 sq ft. In the calculator, enter your depth and read the Coverage Rate card. Multiply sq ft per gallon by the gallons you have.

How many square feet does 5 gallons cover?

It depends on thickness. Five gallons covers 8.02 sq ft at 1 inch deep, 32.1 sq ft at 1/4 inch, and 64.2 sq ft at 1/8 inch. At a 15-mil coating thickness it covers about 535 sq ft. Paint is thinner still. Many interior paint labels list about 350 to 400 sq ft per gallon. At that rate, 5 gallons covers roughly 1,750 to 2,000 sq ft in one coat. The 5-Gal Pail Coverage row gives the exact figure for your depth.

How many square feet does 1 gallon cover?

One gallon covers 1.60 sq ft at 1 inch deep. At 1/4 inch it covers 6.42 sq ft. At 1/8 inch it covers 12.83 sq ft. At 1 mil, one gallon spreads over about 1,604 sq ft. To find coverage at any coating thickness, divide 1,604 by the thickness in mils. A 10-mil coat gives 1,604 ÷ 10 = 160 sq ft per gallon.

Does the calculator use US or imperial gallons?

It uses US liquid gallons at 231 cubic inches each. An imperial gallon is larger, at about 277.42 cubic inches. One square foot at 1 inch deep holds 0.623 US gallons but only 0.519 imperial gallons. To convert a US result to imperial gallons, multiply by 0.8327. Metric mode avoids the issue and reports liters.

Does the result include waste or extra coats?

No. The result assumes one even layer with no loss. Add 5 to 10 percent for waste on smooth surfaces. Add more on porous or rough concrete, which soaks up material. For multiple coats at the same thickness, multiply the total by the number of coats. If the primer and topcoat have different thicknesses, run each one separately and add the totals.