Last updated: July 17, 2026
Gallons per Square Foot Calculator
Creators
Dharmendra SinghReviewers
Creators
Dharmendra SinghReviewers
Quick Answer
The Gallons per Square Foot Calculator converts between liquid volume and base area for rectangular containers using the 7.48052 US gallons per cubic foot conversion. It supports two modes: (1) given base area and depth, compute gallons per sq ft and total volume; (2) given volume and depth, compute the required base area. All common area, height, and volume units are supported with NIST-standard conversion factors.
To find gallons per square foot, multiply the liquid depth in feet by 7.48052. For example, a 4-foot-deep pool holds 29.92 gallons per square foot of base area. Multiply that by the total base area in square feet to get the total volume in gallons.
Key Takeaways
- One cubic foot of water holds exactly 7.48052 US gallons — the foundation of all volume-to-area calculations.
- Gallons per square foot equals depth in feet multiplied by 7.48052, independent of the base dimensions.
- A standard backyard swimming pool (20×40 ft, 4 ft depth) holds approximately 23,938 gallons.
- The calculator supports both forward mode (area+depth→gallons) and reverse mode (volume+depth→area).
- All input units — square meters, liters, inches, centimeters — are converted via NIST-standard factors before calculation.
Creators
Dharmendra SinghReviewers
Creators
Dharmendra SinghReviewers
Formula
Gallons/sq ft = h × 7.48052 | Total Volume (gal) = A × h × 7.48052 | Area (sq ft) = Volume ÷ (h × 7.48052)
Where:
- V=Total Volume(US gallons)
- A=Base Area(square feet)
- h=Liquid Depth or Height(feet)
- k=Conversion factor (1 cubic foot = 7.48052 US gallons)(gal/ft³)
Worked Examples
Swimming Pool Water Volume
Calculate gallons per square foot and total water volume for a rectangular pool.
- 1Convert area to sq ft: 200 sq ft (no conversion needed).
- 2Convert depth to feet: 4 ft (no conversion needed).
- 3Gallons per sq ft = 4 ft × 7.48052 = 29.92 gal/sq ft.
- 4Volume (cu ft) = 200 sq ft × 4 ft = 800 cu ft.
- 5Total volume = 800 cu ft × 7.48052 = 5,984.42 US gallons.
Water Storage Tank
Find the water capacity of an 8 ft × 8 ft base tank that is 6 feet tall.
- 1Base area = 8 ft × 8 ft = 64 sq ft.
- 2Gallons per sq ft = 6 ft × 7.48052 = 44.88 gal/sq ft.
- 3Volume (cu ft) = 64 sq ft × 6 ft = 384 cu ft.
- 4Total volume = 384 cu ft × 7.48052 = 2,872.52 US gallons.
Reverse: Find Required Base Area
Determine the base area needed to hold 1,000 gallons at a depth of 3 feet.
- 1Convert 1,000 US gallons to cubic feet: 1,000 ÷ 7.48052 = 133.68 cu ft.
- 2Gallons per sq ft = 3 ft × 7.48052 = 22.44 gal/sq ft.
- 3Required base area = 133.68 cu ft ÷ 3 ft = 44.56 sq ft.
- 4Verify: 44.56 sq ft × 22.44 gal/sq ft ≈ 1,000 gallons ✓
Introduction
The Gallons per Square Foot Calculator computes how many US gallons of liquid are held per square foot of base area at a given depth. Using the exact conversion factor of 7.48052 US gallons per cubic foot, it supports two modes: (1) calculate total volume from area and depth, or (2) find the required base area from a known volume and depth. It handles multiple area, height, and volume units — making it ideal for swimming pools, storage tanks, aquariums, garden ponds, and any rectangular water vessel.
What Does Gallons per Square Foot Mean?
Gallons per square foot (gal/ft²) expresses volumetric liquid coverage: for every square foot of flat base area, how many US gallons are contained at a specific depth. The relationship is straightforward — it equals the liquid depth in feet multiplied by the 7.48052 conversion factor (the number of US gallons in one cubic foot). A pool filled to 4 feet deep holds 29.92 gallons per square foot of base area, regardless of pool shape (for rectangular pools). This measure is widely used in pool volume calculations and tank capacity planning.
The 7.48052 Gallons per Cubic Foot Conversion Factor
One US liquid gallon equals exactly 231 cubic inches. One cubic foot equals 1,728 cubic inches. Therefore: 1 ft³ = 1,728 ÷ 231 = 7.48051948… ≈ 7.48052 US gallons. This is the exact conversion defined by the NIST Handbook of Chemistry and Physics and underpins every volume–area calculation on this page. For UK (imperial) gallons, the factor is 6.22884 gal/ft³ (since 1 imperial gallon = 277.42 cubic inches).
Two Calculation Modes Explained
Mode 1 — Area + Depth → Volume: Enter the base area (e.g., pool surface in sq ft) and the liquid depth (e.g., 4 feet). The calculator computes gallons/sq ft and total volume. This is useful when sizing pumps, heaters, or chemicals. Mode 2 — Volume + Depth → Area: Enter a known volume (e.g., 5,000 gallons) and a target depth. The calculator returns the required base area in sq ft. This helps engineers design tanks to fit a space while meeting a capacity requirement. The concrete calculator uses a similar area-to-volume approach for slab pours.
Common Applications for Pools, Tanks, and Ponds
- Swimming pools: A standard backyard pool (20 ft × 40 ft, 4 ft avg depth) holds ≈ 23,936 gallons (29.92 gal/ft² × 800 ft²). - Hot tubs and spas: Typical 6 ft × 6 ft tub at 3 ft depth = 22.44 gal/ft² × 36 ft² = 807.8 gallons. - Agricultural water tanks: Square steel tanks rated in gallons can be reverse-calculated to find floor area requirements. - Garden ponds: Determine fish stocking density by knowing exact gallon capacity. - Fire suppression reservoirs: Fire flow calculators require precise storage volumes. For estimating materials like gravel or sand lining a pond floor, pair this tool with the gravel calculator and the paint calculator for waterproof coatings. See also the US Geological Survey water-use overview for context on typical residential water volumes.
Unit Conversion Reference
Area units (converted to sq ft internally): - 1 sq in = 1/144 sq ft (0.006944) - 1 sq yd = 9 sq ft - 1 m² = 10.7639 sq ft - 1 cm² = 1/929.03 sq ft Height units (converted to feet): - 1 in = 1/12 ft - 1 yd = 3 ft - 1 m = 3.28084 ft - 1 cm = 1/30.48 ft - 1 mm = 1/304.8 ft Volume units (converted to US gallons): - 1 L = 0.264172 US gal - 1 ft³ = 7.48052 US gal - 1 in³ = 1/231 US gal - 1 m³ = 264.172 US gal - 1 imp gal = 1.20095 US gal Refer to the NIST Guide to SI Units for authoritative conversion values.
Accuracy and Limitations
This calculator assumes a rectangular (prismatic) container with a uniform base area and vertical sides. Curved, tapered, or irregular shapes require volume integration. For a cylindrical tank, use the pipe volume calculator. Results are computed in double-precision floating-point arithmetic; rounding to two decimal places is applied in displayed outputs. The 7.48052 conversion factor is accurate to six significant figures, matching ASTM and AWWA engineering standards.
Quick Reference Card
Gallons per Square Foot Quick Reference
Quick reference • Gallons per Square Foot Calculator
Gal/sq ft = Depth (ft) × 7.48052Valid range: Depth > 0; Area > 0; valid for any rectangular prismatic container
Common Values
⚠ Watch Out
- •This formula assumes a rectangular (flat-bottomed) container with uniform depth — do not use for sloped pool floors or cylindrical tanks without adjustment.
- •US gallons and UK (imperial) gallons differ by ~20%; always confirm which unit your pump or chemical dosing chart uses.
- •At zero depth the result is zero — always verify depth input is in the correct unit (feet, not inches).
- •Depth entered in inches must be converted to feet (divide by 12) or use the inches unit selector to avoid a 12× error.
Pro Tips
- →For average-depth pools with sloped shallow/deep ends, use the average depth ((shallow + deep) ÷ 2) for a close estimate.
- →To cross-check: 1,000 gallons ÷ 7.48052 = 133.68 ft³; confirm with length × width × depth.
- →Chemical dosing rates expressed in oz per 1,000 gallons can be scaled by dividing total pool gallons by 1,000.
- →For pond volume estimates, multiply this result by 0.9 to account for typical irregular bank slopes reducing effective volume.
FAQs
How many gallons are in one cubic foot of water?
Exactly 7.48051948 US gallons — rounded to 7.48052 for practical calculations. This is derived from 1 ft³ = 1,728 in³ and 1 US gallon = 231 in³, giving 1,728 ÷ 231 = 7.48052.
How do I calculate total gallons in a swimming pool?
Multiply the base area (in sq ft) by the average depth (in ft) to get cubic feet, then multiply by 7.48052. For example: 20 ft × 40 ft × 4 ft average depth = 3,200 ft³ × 7.48052 = 23,938 gallons.
What is gallons per square foot used for?
It is used to determine how much liquid a container holds relative to its floor space. Common uses include pool chemical dosing (per sq ft rates), irrigation coverage, waterproofing product estimating (gallons applied per sq ft), and comparing tank efficiencies.
Can I use this calculator for metric measurements?
Yes. Select square meters or cm² for area, and meters or cm for depth. The calculator converts all inputs to US customary internally using standard NIST conversion factors, then computes the result.
How accurate is the 7.48052 conversion factor?
The US gallon is defined as exactly 231 cubic inches. One cubic foot is exactly 1,728 cubic inches. Therefore 1 ft³ = 1,728/231 = 7.48051948… US gallons. Rounding to 7.48052 introduces an error of less than 0.00001%, which is negligible for practical engineering work.
How do I find the base area needed for a specific volume?
Switch to 'Volume + Depth → Area' mode, enter your target volume (in gallons or other units) and the planned depth. The calculator computes: Area = Volume(gal) ÷ (Depth(ft) × 7.48052). For 1,000 gallons at 3 feet depth: Area = 1,000 ÷ 22.44 = 44.56 sq ft.