Grout Pen Calculator: How Many Pens Do I Need?
Grout lines are hard to estimate by eye: a modest 50 square foot backsplash of subway tile hides well over 150 linear feet of joints. Enter your area and tile size below and the calculator converts it into linear feet of grout and the number of standard pens to buy, including a 10 percent buffer for porous grout and touch-ups.
Estimated grout lines
Recommended pens (standard 5mm tip)
How the math works
The calculator divides your area by the face size of one tile to count tiles, then credits each tile with half its perimeter (joints are shared between neighbors). A 12 x 12 inch tile contributes about 2 linear feet of grout, so a 100 square foot floor holds roughly 200 linear feet. A standard 5mm pen is rated around 150 linear feet per coat in practice, less on wide or thirsty joints, which is why the result includes a 10 percent buffer.
Buying for a color change? Read how to choose a grout pen first, and prep the lines properly with the cleaning guide so the coats you counted are the coats you need.