Flagstone Calculator for a Patio or Path

Calculate flagstone for your patio

Start with the area you’re paving, not the yard it sits in. Length times width for a rectangle. For a circle, measure across the middle and the tool takes it from there. Odd shapes are easiest broken into two rectangles and added together.

Then take back out anything you’re not paving under. A flagstone fire pit area is the usual case, and a 4 ft ring removes about 13 sq ft, which is a real chunk of a small patio. Planters, a tree, a raised bed: same treatment. Measure the finished outside of the feature rather than the opening in the middle of it.

Fire pits are worth a second thought while you’re here. Most flagstone fire pit area ideas put the pit dead center in a circle, which looks right and wastes stone, because every piece around the ring gets cut on two curves. Setting the pit off to one side of a rectangle costs less and leaves somewhere to put chairs. Either way, keep 3 to 4 ft of paving all round the pit so nobody is standing on grass while they poke the fire.

Now the conversion. Coverage per ton comes from the weight of a square foot of the stone, which is its density times its thickness:

lb per cu ft × thickness in inches ÷ 12 = lb per sq ft.

2,000 ÷ lb per sq ft = square feet per ton.

Sandstone at 1.5 in works out at 18.1 lb a square foot, so a ton covers about 110 sq ft. A 16 by 12 patio is 192 sq ft, which needs 1.7 tons of stone laid edge to edge. Add the offcuts and you’re ordering nearer 2.1 tons. That last step is the one people skip, and it’s the reason patios run short.

How much does a pallet of flagstone cover?

A 1.5 ton pallet covers about 166 sq ft of patio at the standard 1.5 in thickness. Go thinner and the same pallet stretches to 248 sq ft. Go up to 2 in stone and it only does 124.

Read the last two columns together and the pattern is simple: every time thickness doubles, coverage halves. There’s nothing clever in it. You’re buying weight, and a thicker slab uses up more weight covering the same square foot of ground. So 1 ton of flagstone covers 166 sq ft at an inch thick, and 1 ton flagstone coverage drops to just 55 sq ft once you move up to 3 in steppers.

One warning about buying flagstone by the pallet. A pallet is not a unit of measurement, it’s a wooden platform, and yards load them to whatever weight suits their forklift. So flagstone pallets vary from yard to yard, and 1 pallet of flagstone at one supplier can be a third heavier than the next one down the road. Ask what theirs comes in at. Being told “about a pallet and a half” is useless information until you know whether a flagstone pallet there is 1.5 tons or 2.5.

Pallets vs tons, and which one your supplier will quote

Tons are the real unit. Pallets are packaging. Almost every yard prices by the ton, then delivers however many pallets that works out to. So a quote often reads as an odd fraction rather than a round count.

Where it matters is the remainder. Order 2.6 tons and you might be sold two pallets of flagstone and a loose half ton in a bucket, or you might be told to take three. Ask up front whether they’ll break a pallet. Most will, and on a small patio the difference is easily $200. Pallet flagstone that arrives strapped and banded is also easier to check: you can see the thickness range and the color across the whole load before anybody cuts the straps.

Two rows are worth memorizing, because they come up constantly. 100 square feet of flagstone is about 1.1 tons with waste allowed. 200 square feet of flagstone is roughly 2.2 tons. Everything else scales straight off those.

A 200 sq ft patio, which is a decent seating area for a table and six chairs, comes out at 2.18 tons. That’s a pallet and a half, and about $653 of sandstone before anything else. Double the patio to 400 sq ft and everything doubles with it, since flagstone has no economy of scale in the quantity. The savings show up in delivery instead, which is charged per trip.

Thickness affects coverage more than anything else

Pick your stone and you move coverage by maybe 20%. Pick your thickness and you move it by 200%. Yet thickness is the spec that gets left to the yard. And most people don’t think about it at all, even though it’s the one that decides the bill.

So choose it on how the patio is being built. Mortared onto an existing concrete slab? 1 in is plenty, and even three quarters works. The slab carries everything and the stone is only a facing. Dry-laid on gravel and sand, you want 1.5 to 2 in. Anything thinner will eventually bridge a soft spot and crack across the middle.

Steppers are the exception at the top end. A stone dropped into a lawn has no support around its edges. And it gets stepped on off-center all day. So 2 to 3 in is normal there. It also has to sit heavy enough not to rock, and mass is what does that.

One practical note. Split stone is sold in a thickness band, not an exact figure, because a single piece varies across itself. A pallet labeled 1 to 1.5 in holds plenty of both. Work from the middle of the band, and if you’re close to a pallet boundary, order the extra.

How much flagstone weighs per square foot

Pounds of flagstone per square foot comes out at about 18.1 for 1.5 in sandstone. That figure does more work than you’d think. Is a single piece a two-person lift? Is your trailer legal loaded? Can a roof deck take it? All three come off that one number.

Sandstone is the lightest and slate the heaviest, and the spread across the whole table is only about 21%. That’s worth knowing but it isn’t worth choosing on. Price varies far more than weight does, and so does what the stone looks like wet.

Where the number bites is in handling. A single piece 2 ft by 3 ft is 6 sq ft, so over 110 lb in sandstone and nearer 130 lb in slate. Carry those on edge with two people, never flat, and never on a slope. And check your trailer rating before loading a pallet: 1.5 tons is 3,000 lb, which is more than most homeowner trailers are plated for.

Waste factor for cutting and fitting, and how much to add

Add 20% for irregular stone laid tight, 8% for squared stone in a pattern. Nobody quantifies this and it’s the difference between one delivery and two.

The reason irregular costs so much more is obvious once you’ve laid some. Every piece has to meet its neighbor along a line that doesn’t exist yet. So you trim one edge, turn it, trim another. The bits that come off are gone. Do that across a whole patio and a fifth of the pallet ends up as rubble. Squared stone only needs cutting where the patio meets its own border.

Notice that open joints cut the waste back to 12%. Widen the gaps to 2 in, fill them with gravel or thyme, and the awkward shapes fit without being trimmed. So you buy less stone and do less cutting. It’s the cheapest version of this patio, and plenty of people prefer how it looks.

Keep the offcuts, incidentally. Broken flagstone is exactly what you want for a small path, a step, or the edge of a bed, and you’ve already paid for it by the ton.

Base and jointing material: what goes under and between

A dry-laid patio is three layers and the stone is only the top one. Underneath goes 4 in of compacted crushed stone, then 1 in of bedding sand screeded flat. The base carries the load and drains. The sand lets you set each irregular piece level despite its varying thickness.

For 200 sq ft that’s roughly 2.5 cubic yards of base stone and about a yard of bedding sand, which is a real material order in its own right. The gravel calculator sizes the base course and bedding sand is worked out here if you want the tonnage for both.

Never lay flagstone straight on soil. It looks fine in September and by April the stones sit at six different heights, because soil holds water, water freezes, and the ground lifts unevenly. That single shortcut is behind most of the wobbly patios people end up re-laying.

Joints are the last decision. Polymeric sand sets firm and keeps weeds down, and flagstone drinks it: about one bag per 25 sq ft, against 100 for tight-jointed pavers. So a 200 sq ft patio takes around 8 bags. The alternative is loose filler, and pea gravel between flagstone is the usual choice there, or soil and a low creeping plant if you want it green.

Flagstone cost per ton, per pallet and installed

Stone runs $200 to $600 a ton depending on the type and how far it travelled. Sandstone sits near $300, bluestone nearer $500, and the harder decorative stones climb from there. On a 1.5 ton pallet that’s $450 to $750 a pallet.

Freight is the part that moves most. Flagstone is quarried in a handful of regions, so Pennsylvania bluestone is reasonable in New Jersey and expensive in Arizona, while Arizona sandstone is the other way round. Buying whatever your local yards stock deepest is usually a third cheaper than specifying a stone by name.

For a 200 sq ft patio, the stone alone is around $653. Add the base and bedding at $150 to $300, jointing sand at $20 a bag, and delivery at $75 to $200. Doing the work yourself, you’re looking at something near $1,053 all in.

Installed is a different order of number. Contractors charge $18 to $35 a square foot for dry-laid flagstone, so that same 200 sq ft patio is $3,600 to $7,000. Most of the gap is labor, and irregular stone sits at the top of the range because fitting it is slow, skilled work that no machine helps with.

Related calculators

• Bedding sand and polymeric joint sand, both sized for the same patio you just measured.
• Base stone by grade and tonnage for the 4 inch course that goes underneath.
• Filling flagstone joints with pea gravel, which sizes the gaps rather than the whole patio.
• Weight and cost of landscaping boulders if the patio is being edged or framed with larger stone.
• The general sand calculator for anything the paving job needs beyond the bedding course, by the yard, the ton or the bag.
• The full set of stone calculators, which is the quickest way to price a hardscape job end to end.