Flagstone Calculator
Estimate how many tons of flagstone to order for a patio, walkway or stepping-stone path. Enter the area and the stone thickness and get the stone weight, the coverage per ton, the gravel and sand for the base, and the bags of joint filler.
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Add up several sections for an L-shape or a path.
10% is typical for irregular stone; 15% for lots of cutting.
4 in for patios and paths, 6 in in clay or frost areas.
Per US ton, or per tonne in metric.
Per 50 lb / 22.7 kg bag of filler.
How to use the Flagstone Calculator
- Enter the area as length × width, a circle diameter or a known square footage.
- Pick the stone type and thickness range your stone yard sells, e.g. 1½–2 in.
- Choose the joint spacing and an extra allowance for cutting and shaping.
- Select how it will be installed: on gravel and sand, mortared on concrete, or set in soil.
- Read the results: tons of flagstone, base materials and bags of joint filler, plus cost if you add prices.
How the flagstone calculator works
Stone weight = area × (1 − joint share) × (1 + extra %) × average thickness (ft) × density (lb/ft³) ÷ 2,000 = US tons.
Coverage per ton = 2,000 ÷ (density × thickness ÷ 12), then divided by (1 − joint share) for the patio area including joints.
Base: gravel = area × depth ÷ 12 × 1.15 (compaction) at about 104 lb/ft³ (1.4 tons per cubic yard); sand = area × depth ÷ 12 × 1.10 at about 100 lb/ft³. Joint filler = area × joint share × stone thickness, plus 10%.
Example: a 12 × 14 ft patio (168 sq ft) in 1½–2 in sandstone with 1 in joints: 168 × 0.90 × 1.10 = 166 sq ft of stone × 1.75/12 = 24.3 cu ft × 145 lb = 3,520 lb ≈ 1.76 tons. The 4 in gravel base is about 3.3 tons and the 1 in sand bed about 0.8 tons.
Approximate flagstone coverage per ton
Patio area covered by one US ton of stone at about 145 lb/ft³ (sandstone) with 10% of the area in joints, before the extra allowance. Denser stone covers less.
| Stone thickness | Average | Sq ft per ton (stone only) | Patio sq ft per ton (10% joints) |
|---|---|---|---|
| 1 – 1½ in | 1¼ in | ~132 | ~147 |
| 1½ – 2 in | 1¾ in | ~95 | ~105 |
| 2 – 2½ in | 2¼ in | ~74 | ~82 |
| 2½ – 3 in | 2¾ in | ~60 | ~67 |
Tips for ordering flagstone
- Choose thicker stone for dry-laid patios. 1½–2 in or thicker resists cracking on a gravel and sand bed; thinner 1 in stone is usually mortared onto a concrete slab.
- Ask for the yard's own coverage figure. Thickness varies stone to stone, so the actual coverage of a pallet can differ from the estimate.
- Pallet weight matters. A pallet often holds 1–2 tons; make sure the delivery truck can reach the site and the ground can take the load.
- Slope the patio about ⅛–¼ in per foot away from the house so water drains off the surface.
- Lay out the stones before setting them to plan joints and keep the largest stones for high-traffic spots and edges.
Frequently asked questions
How many square feet does a ton of flagstone cover?
It depends mostly on thickness. A ton of 1½–2 in sandstone flagstone (about 145 lb per cubic foot) covers roughly 95 sq ft of stone, or about 105 sq ft of patio once 10% joints are included. Thinner 1–1½ in stone covers about 130–145 sq ft per ton, and 2½–3 in stone only about 60–67 sq ft.
How do I calculate how much flagstone I need?
Multiply the area by the share of the area that will be stone (for example 0.9 with 10% joints), add 10% for cuts, multiply by the average thickness in feet to get cubic feet, then multiply by the stone density and divide by 2,000 for tons. A 12 × 14 ft patio with 1¾ in sandstone needs 168 × 0.9 × 1.1 × 1.75/12 × 145 ÷ 2,000 ≈ 1.75 tons.
How much does flagstone weigh?
Solid flagstone weighs about 140–175 lb per cubic foot depending on the rock: sandstone around 145, limestone around 155, bluestone around 160, quartzite and slate around 165–170. A square foot of 1½ in sandstone weighs roughly 18 lb.
What base do I need under a flagstone patio?
For a dry-laid patio, the usual build-up is 4 in of compacted crushed gravel (6 in on clay or where the ground freezes) topped with a 1 in bed of coarse sand or stone dust to set the stones. Paths with light foot traffic can use a thinner base; stepping stones can be set straight into the soil.
How much extra flagstone should I order?
Order about 10% extra for irregular flagstone so you can choose good fits and trim edges. Allow 15% or more when the design needs a lot of cutting, such as a straight border or many curves.
What goes between flagstone joints?
Common joint fillers are polymeric sand, stone dust or decomposed granite, mortar for mortared patios, and soil for creeping thyme, moss or grass. Polymeric sand hardens when wetted and resists weeds and washout in joints up to about 1–2 in wide; check the product's maximum joint width.
Is flagstone sold by the ton or by the square foot?
Most stone yards sell natural flagstone by the ton or by the pallet, while some sell gauged (cut, even-thickness) flagstone by the square foot. Ask the supplier for their coverage per ton for the exact stone, since thickness and density vary between quarries.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.