Grout Calculator
By Taro Schenker | Updated February 11, 2026
Quick Answer: To calculate grout, use the formula: Grout (cu in/sq ft) = 144 x Joint Width x Tile Thickness x (Tile Length + Tile Width) / (Tile Length x Tile Width). Multiply by total area, add 10% waste, then convert to pounds using grout density of 100 lbs/cu ft (divide cu in by 1,728 first). Divide weight by 25 for the number of standard 25 lb bags. For 100 sq ft of 12 x 12 in tile with 1/8 in joints and 3/8 in thickness, you need about 1 bag of grout.
Calculate how much grout you need for your tiling project. Enter your tile dimensions, joint width, and area to get the exact number of bags, total weight, and estimated cost.
How to Calculate Grout
The formula for calculating grout volume per square foot is:
- Measure your tile length, width, and thickness in inches.
- Determine your grout joint width (the gap between tiles).
- Calculate the total area to be tiled in square feet.
- Apply the formula to find grout volume per square foot, then multiply by the total area.
- Convert volume to weight using grout density (about 100 lbs per cubic foot).
- Add 10% for waste and divide by bag size to get the number of bags needed.
Grout Coverage by Tile Size
Quick reference for how many 25 lb bags of grout you need per 100 square feet at common tile sizes and joint widths:
| Tile Size | Joint Width | Bags per 100 sq ft |
|---|---|---|
| 4" × 4" | 1/8" | 2 bags |
| 6" × 6" | 1/8" | 1 bag |
| 12" × 12" | 1/8" | 1 bag |
| 12" × 12" | 1/4" | 1 bag |
| 12" × 24" | 1/8" | 1 bag |
| 24" × 24" | 1/8" | 1 bag |
Sanded vs Unsanded Grout
- Sanded grout: Best for joints wider than 1/8 inch. The sand filler adds strength and reduces shrinkage. Use for floor tiles, larger format wall tiles, and outdoor installations.
- Unsanded grout: Best for joints 1/8 inch or narrower. Its smooth texture works well with polished marble, glass tile, and other scratch-sensitive surfaces.
- Epoxy grout: The most durable option — fully waterproof and stain-proof. Ideal for showers, kitchen backsplashes, and commercial applications. More expensive and harder to work with than cement-based grout.
Formula Summary
Grout Volume Formula: To calculate grout needed per square foot of tiled area, use the joint geometry formula that accounts for tile size, joint width, and tile thickness (joint depth).
$$V_{\text{cu in/sq ft}} = \frac{144 \times J_w \times T_d \times (T_L + T_W)}{T_L \times T_W}$$
Total Grout: $$V_{\text{total}} = V_{\text{cu in/sq ft}} \times A \times (1 + W_f)$$
Weight Conversion: $$W_{\text{lbs}} = \frac{V_{\text{total}}}{1728} \times 100$$ (1 cu ft = 1,728 cu in; grout density = 100 lbs/cu ft)
Bags Formula: $$\text{Bags}_{25\text{lb}} = \lceil \frac{W_{\text{lbs}}}{25} \rceil$$
| Constant | Value |
|---|---|
| Grout density | 100 lbs/cu ft |
| Standard bag size | 25 lbs |
| Cu in per cu ft | 1,728 |
| Sq in per sq ft | 144 |
| Default waste factor | 10% |
Standard Assumptions: Joint depth equals tile thickness. Waste factor of 10% accounts for uneven joints, cleanup loss, and mixing waste. Grout density of 100 lbs/cu ft applies to both sanded and unsanded cement-based grout. Sanded grout is used for joints wider than 1/8 inch; unsanded for 1/8 inch or narrower.
Related Calculators
- Tile Calculator — calculate how many tiles you need for your project
- Paver Calculator — estimate pavers for patios, walkways, and driveways
Estimates are for planning purposes only. Consult a qualified contractor for critical projects. Actual material requirements may vary based on site conditions, waste, and installation methods.
Pricing last verified: February 2026. Material prices vary by region, season, and supplier. Prices shown are national averages for planning purposes.