Paving Slab Calculator
Estimate paving slab quantities, square footage coverage, extra allowance for cuts, and total full packs needed for patios, paths, and walkways.
Paved Area Measurements
Choose units and enter your patio or walkway dimensions.
Slab Face Size & Packs
Enter the individual slab size and supplier pack details.
Planning estimate only. Slabs per pack and face dimensions vary by manufacturer. Always verify pallet coverage.
Your Estimate
Required slab count and coverage summary.
How It Is Calculated
Large format slabs (e.g., 24×24 inch or 600×600 mm) are more prone to transit breakage than small pavers. Keeping 5%–10% extra ensures you have intact slabs for perimeter trimming and future replacements.
Standard Slab Sizes
Common residential patio slabs come in 24×24 in, 18×18 in, 12×24 in (or metric 600×600 mm, 450×450 mm, and 900×600 mm). Larger slabs install faster but require two people or vacuum lifters to position safely.
Pack & Crate Purchasing
Suppliers rarely break open shrink-wrapped patio packs. When calculating your total order, always round up to the nearest full pack to ensure your slabs originate from the same manufactured color dye batch.
How to Calculate Paving Slabs for Patios, Paths & Terraces
Installing paving slabs (often called patio flags or flagstones) transforms backyard living areas into functional outdoor rooms. Ordering the exact quantity requires measuring the project footprint, determining the face area of each slab, and accounting for edge cuts around borders and obstacles.
1. Measuring Your Planned Paving Area
Measure the outer length and width of the patio boundary. For a rectangular layout, multiply length by width to obtain total square footage. For L-shaped terraces or stepped patios, divide the site into separate rectangular sections, calculate the square footage for each section, and sum them together.
2. Determining Slab Face Area
Check the actual face dimensions of your selected slab. In US Customary units, multiply the slab length in inches by slab width in inches and divide by 144 to get square feet per slab. In Metric units, convert millimeters to meters before calculating coverage area.
Paving Slab Calculation Formulas (Step-by-Step)
Use the following formulas to calculate slab quantities manually:
US Customary Formulas (Feet, Inches, Slabs)
1. Paved Area: Area (sq ft) = Length (ft) × Width (ft)
2. Area with Cut Allowance: Order Area = Paved Area × (1 + Allowance % ÷ 100)
3. Single Slab Face Area: Slab Area (sq ft) = [Length (in) × Width (in)] ÷ 144
4. Slabs Required: Total Slabs = Round Up (Order Area ÷ Single Slab Area)
5. Full Packs Needed: Total Slabs ÷ Slabs per Pack (Round Up to next integer)
Metric Formulas (Meters, Millimeters, Slabs)
1. Paved Area: Area (m²) = Length (m) × Width (m)
2. Area with Cut Allowance: Order Area = Paved Area × (1 + Allowance % ÷ 100)
3. Single Slab Face Area: Slab Area (m²) = [Length (mm) × Width (mm)] ÷ 1,000,000
4. Slabs Required: Total Slabs = Round Up (Order Area ÷ Single Slab Area)
5. Full Packs Needed: Total Slabs ÷ Slabs per Pack (Round Up to next integer)
3. Choosing an Extra Allowance for Cuts & Waste
Unlike small pavers, cutting large patio slabs creates larger unrecoverable off-cuts. A simple square patio with straight borders typically needs a 5% to 8% allowance. If your patio incorporates curves, diagonal patterns, or diagonal steps, budget a 10% to 15% allowance.
4. Joint Spacing Considerations
This calculator estimates quantities based on the nominal face dimensions of the slabs. If you are using wide pointing mortar joints (such as 3/8 inch or 10 mm joint gaps), the slabs will cover slightly more area, providing a comfortable buffer against running short.
Frequently Asked Questions
How many paving slabs do I need per square meter?
For standard 600×600 mm slabs, you need roughly 2.8 slabs per m². For 450×450 mm slabs, you need approximately 5 slabs per m².
How many 24x24 inch slabs are in 100 square feet?
Each 24×24 inch slab covers exactly 4 sq ft. To cover 100 sq ft without waste, you need 25 slabs. With a 10% cut allowance, order 28 slabs.
Do I have to buy full packs of slabs?
Most quarries and hardscape distributors sell patio flags only in full banded crates. Ordering whole packs protects slabs during transit and guarantees a uniform color lot.
Can I calculate slabs using metric measurements?
Yes. Select "Metric" in the dropdown to enter patio length and width in meters, and slab dimensions in millimeters.
How much extra should I allow for cutting?
A standard rectangular patio requires 5%–10% extra. Curved edges, intricate borders, and diagonal layouts require 10%–15%.