Subway Tile Grout Calculator
Pre-filled for 3×6 subway tile with 1/16 in unsanded joints — the classic backsplash setup. Enter area to get pounds and bag count. Adjust any input for your specific tile.
Tile & Area
Grout Joint
Grout Type & Bag Size
How the grout formula works
Step 1 — joint length per unit area (TCNA/Laticrete geometry)
joint_len_per_area = (tile_L + tile_W) / (tile_L × tile_W) [1/in] Each tile shares half its perimeter with its neighbours, netting (L+W) of joint per tile face area L×W. A 12×12 yields 24/144 = 0.167/in; a 2×2 mosaic yields 4/4 = 1.0/in — 6× more grout for the same area.
Step 2 — grout weight per square foot
lb/sq ft = joint_len_per_area × joint_width × joint_depth × density (lb/in³) × 144 Density: sanded 104 lb/ft³ (= 0.0602 lb/in³), unsanded 90 (= 0.0521), epoxy 110 (= 0.0637). Multiplying by 144 in²/ft² converts the per-in² result to per-ft².
Step 3 — total pounds and bags
grout_lb = lb/sq ft × area × (1 + waste%/100) bags = ⌈ grout_lb / bag_size − 1e−9 ⌉ The −1e−9 float guard prevents a spurious extra bag when the result lands on exactly a whole number due to floating-point rounding.
Classic subway tile uses very little grout compared to mosaic tile — narrow 1/16 in joints at 5/16 in depth use about 0.073 lb per square foot of unsanded grout. A typical 30 sq ft backsplash needs under 3 lb with waste, fitting easily in one 8 lb bag.
Related tools
Frequently Asked Questions
Classic 3×6 subway tile with a 1/16 in unsanded joint at 5/16 in depth (unsanded grout, 90 lb/ft³): the coverage rate is about 0.073 lb/sq ft. For a 30 sq ft backsplash with 10% waste that is roughly 2.4 lb — well under one 8 lb bag. Standard kitchen backsplashes use very little grout because the joints are narrow.
Typically unsanded. Most subway tile backsplashes use 1/16 in joints — the minimum standard grout-joint width — which require unsanded grout. If you are doing a floor or shower with 1/8 in or wider joints — sometimes chosen for a handmade-look or rustic pattern — switch to sanded grout. The calculator warns you if your joint width and grout type combination is mismatched.
Standard 3×6 ceramic subway tile is typically 5/16 in thick; glass subway tile is often 3/16 to 1/4 in. The joint depth equals the tile thickness — the joint is filled from the substrate surface up to the tile face. Enter your actual tile thickness for the most accurate result.
A running bond (also called "brick pattern") offsets each row by half a tile length — 3 in for 3×6 tile. This is the most common subway tile layout. It does not significantly change grout consumption vs a straight stack because the joint length per sq ft is the same; the difference only shows in cut tile waste at edges (use 15% waste for a running bond in irregular spaces).
This page pre-fills tile size to 3×6 inches and joint width to 1/16 in unsanded — the classic subway tile backsplash setup. You can adjust any input. The formula is identical to the main grout calculator; it uses the same shared component and the same TCNA/Laticrete volume formula.