Concrete quantity toolsMeasure the area you will coat
Use surface area, not the volume of concrete beneath it. A 20-foot by 30-foot rectangle has a top surface area of 600 square feet. Include vertical faces only if you plan to coat them, and subtract areas that will remain untreated. Slab thickness alone does not add those faces to the estimate.
For each area, note the product, surface condition, coverage units, and whether the stated rate is per coat or for the full system. Coverage can differ between coats and between new and previously sealed concrete. Temperature, texture, and porosity can also affect the amount needed, so retain the conditions attached to the product's rate when you record it.
Separate areas that use different coverage rates
List the surfaces you intend to coat, such as the slab top, exposed edges, or wall faces. Combine areas only when the same product instructions and per-coat rate apply. Keep separate groups when the product data gives different coverage for a surface, condition, or coat.
For example, if a 600 ft² slab top and an 80 ft² edge use the same product and rate, calculate them as 680 ft². If the edge has a different rate, calculate the top and edge separately and add the gallons. The calculator accepts one area and one rate at a time.
Calculate gallons for each coat
For each coat, divide the area in square feet by the coverage in square feet per US gallon. At an example coverage range of 300–400 square feet per gallon, 600 square feet needs 600/400 to 600/300, or 1.5–2 gallons. Carry the range forward unless the product data and surface conditions support a more specific rate; averaging the endpoints can hide how much the result may vary.
If a second coat has an example coverage rate of 500 square feet per gallon, it adds 1.2 gallons. The total is then 2.7–3.2 gallons. These rates are examples, not product recommendations. This calculator uses one coverage rate for all coats. If rates differ, calculate each coat separately and add the results.
Round the total to whole containers
For the 2.7–3.2-gallon example, one-gallon containers would require three to four containers: three cover the lower estimate, while four cover the upper estimate. If the product is available only in five-gallon containers, one container covers either end of the range. Record both the gallons needed and the container capacity you are buying so the unused amount is clear.
Check whether the product’s coverage rate applies to one coat or the entire coating system. Do not multiply an entire-system rate by the number of coats again. Keep any waste allowance separate from uncertainty in coverage. Gallons alone do not establish product compatibility, the right number of coats, or when the surface is ready for application.