What This Calculator Does
The Countertop Square Footage Calculator helps you estimate how much surface area your kitchen or bathroom countertops cover. Because countertops are rarely a single rectangle — they often include an L-shaped run, an island, and a peninsula — this tool lets you enter up to three separate sections. It adds the area of each section, converts the total to square feet, and adds an optional waste allowance for cuts, sink cutouts, and breakage.
How to Use It
Measure the length and width of each straight countertop section in inches. Enter each section as a separate length × width pair. If you only have one or two sections, leave the unused fields at zero. Add a waste percentage (10% is a common allowance for fabricators) and the calculator returns total square footage, square meters, and total square inches.
The Formula Explained
Each section's area is its length multiplied by its width. The total area in square inches is the sum of all sections: \(A = \Sigma(\text{length} \times \text{width})\). To get square feet, divide by 144 (since one square foot is \(12 \times 12 = 144\) square inches). Finally, multiply by \(\left(1 + \frac{\text{waste}}{100}\right)\) to account for material overage.
$$\text{Area} = \frac{\text{L}_1\cdot\text{W}_1 + \text{L}_2\cdot\text{W}_2 + \text{L}_3\cdot\text{W}_3}{144} \times \left(1 + \frac{\text{Waste \%}}{100}\right)$$
Worked Example
Say you have a main run 108 in × 25 in and an island 60 in × 25 in. Section areas are 2,700 in² and 1,500 in², totaling 4,200 in². Dividing by 144 gives 29.17 sq ft. Adding 10% waste gives 32.08 sq ft — the amount of slab material to order.
$$\text{Area} = \frac{108 \times 25 + 60 \times 25}{144} \times \left(1 + \frac{10}{100}\right) = \frac{2{,}700 + 1{,}500}{144} \times 1.1 = \frac{4{,}200}{144} \times 1.1 = 29.17 \times 1.1 = 32.08 \text{ sq ft}$$
FAQ
Why add a waste percentage? Slabs are cut to fit, and offcuts, sink/cooktop openings, and breakage mean you typically need 5–15% more material than the finished surface.
Should I measure in inches or feet? This tool expects inches because countertops are usually measured that way; it converts to square feet for you.
What about backsplashes? Add a backsplash as one of the section fields (its length × height) if you want it included in the total.
