Calculator
Stucco Calculator
A bag of stucco doesn't cover a fixed number of square feet — it covers a fixed volume, and the area that volume spreads over depends entirely on how thick you trowel it. A bag rated at 27 square feet at 3/8 inch covers 40.5 square feet at 1/4 inch and only 20.25 at 1/2 inch, and it's the same bag in every case. A coverage figure quoted without a thickness attached to it isn't a complete number, and most stucco calculators quote exactly that.
This one keeps two products separate the way the job actually is: a base coat, applied at whatever combined thickness your system calls for, and a finish coat, which is a different product with its own reference thickness and its own coverage figure. It also only counts lath when the system needs it — a three-coat job over open framing does, a two-coat job bonded directly to solid masonry does not — instead of quoting one lath number regardless of substrate.
Calculate your quantity
Stucco that hits the ground instead of the wall still came out of a bag.
Base coat bags
22 80 lb bags
Finish coat bags
5 80 lb bags
- Stucco area
- 270 sq ft
- Base coat thickness
- 0.75 in
- Base coverage per bag
- 13.5 sq ft
- Lath sheets
- 17 sheets
- Total applied volume
- 19.7 cu ft
- Three-coat over lath: scratch, brown, then finish.
Shopping summary
- • 22 bags of base coat stucco
- • 5 bags of finish coat
- • 17 sheets of metal lath
This is an estimate — confirm structural work with a professional.
How this calculation works
The base coat's thickness depends on which system you're running. A three-coat system over lath is a scratch coat plus a brown coat, and their combined depth is what the bag's coverage scales against. A two-coat system over solid masonry skips the scratch coat entirely — the masonry itself provides the key the scratch coat would otherwise create — so only the brown coat thickness counts. Coverage per bag then scales inversely from a reference: an 80 lb bag rated at 27 square feet at 3/8 inch covers 27 x (0.375 ÷ your thickness) square feet at whatever thickness you're actually applying.
The finish coat is a separate product entirely, with its own reference thickness and its own coverage figure — 70 square feet at 1/8 inch is typical, and it scales the same inverse way the base coat does. It is not a fraction of the base coat's coverage, and running the two through the same rate is a common way to under-order finish or over-order base. Lath, where the system needs it, is figured last: metal lath sheets net out to roughly 16 square feet of usable coverage each once the laps at every edge and end are accounted for, well under a sheet's nominal size.
- Coverage moves inversely with thickness, not linearly with area — doubling either coat's thickness halves that coat's coverage per bag, full stop.
- The scratch coat only exists, and only costs bags, in the three-coat lath system; the two-coat masonry system's thickness field for it goes unused because there's nothing to scratch into.
- Base and finish are different products with different coverage references — never assume one bag count applies to both.
- Lath is zero for a system bonded directly to solid masonry and non-zero for a system built over open framing; get the system selection right before trusting either bag count.
The formula
baseBags = (area × (1+waste)) ÷ baseCoverage, baseCoverage = 27 × (0.375 ÷ baseThickness); finishBags = (area × (1+waste)) ÷ finishCoverage, finishCoverage = 70 × (0.125 ÷ finishThickness)
- baseThickness
- Combined depth of the coats applied before finish: scratch plus brown for a three-coat lath system, or brown alone for a two-coat system over solid masonry, since the masonry substrate stands in for what the scratch coat would otherwise provide.
- baseCoverage
- Square feet one 80 lb bag of base coat covers at your baseThickness, scaled inversely from the reference figure of 27 sq ft at 3/8 inch.
- finishCoverage
- Square feet one 80 lb bag of finish coat covers at your finish thickness, scaled from its own reference of 70 sq ft at 1/8 inch — a different product with a different starting point from the base coat.
- lathSheets
- Metal lath sheets for a three-coat system over open framing, at roughly 16 sq ft of usable coverage per sheet after the laps every edge and end needs. Zero for the two-coat masonry system, which has no lath in it at all.
- area
- Net wall area — gross wall footprint less door and window openings — shared by both the base and finish coat calculations.
The two products are kept on entirely separate coverage arithmetic on purpose. A brown coat troweled to 1/2 inch and a finish coat troweled to 1/8 inch are not the same material at different thicknesses — they're different products with different aggregate sizes and different published yields — so scaling one number to cover both, which a simpler calculator sometimes does, produces a bag count that's wrong for whichever coat wasn't the reference.
Where these numbers come from
- 27 sq ft per 80 lb bag at 3/8 in for base/scratch coat stucco
- Manufacturer-published reference coverage for a typical base coat product at its stated application thickness. Used as the fixed point the inverse-thickness scaling is built from, not as a constant coverage figure.
- 70 sq ft per 80 lb bag at 1/8 in for finish coat stucco
- Manufacturer-published reference for a separate finish coat product line, at its own stated thickness. Finish coat is a different formulation from base coat and does not share its coverage figure.
- ~16 sq ft net coverage per lath sheet
- Trade convention. Metal lath sheets are nominally about 27 x 97 in, roughly 18 sq ft, but installation laps every edge and end, so usable coverage runs lower than the sheet's raw dimensions — treat 16 as a working estimate, not a manufacturer spec.
- 10% waste
- Trade convention for hand or hopper-applied stucco, covering overspray, board loss, and the material left in a mixer that never makes it to the wall.
Worked examples
A 32 by 9 foot three-coat wall over lath, with a garage door
| Wall length | 32 ft |
|---|---|
| Wall height | 9 ft |
| Opening area | 63 sq ft |
| System | Three-coat over lath |
| Scratch coat | 0.375 in |
| Brown coat | 0.375 in |
| Finish coat | 0.125 in |
| Waste factor | 10 % |
| Base coat bags | 19 80 lb bags |
|---|---|
| Finish coat bags | 4 80 lb bags |
| Stucco area | 225 sq ft |
| Base coat thickness | 0.75 in |
| Base coverage per bag | 13.5 sq ft |
| Lath sheets | 15 sheets |
| Total applied volume | 16.4 cu ft |
The garage door takes 63 square feet off a 288 square foot wall, leaving 225 to coat. Scratch and brown together put down 3/4 inch of base coat, which is double the 3/8 inch reference — so coverage per bag is halved to 13.5 square feet, and 225 square feet at 10% waste needs 19 bags. The finish coat, applied right at its own 1/8 inch reference, needs no scaling at all: the full 70 square feet per bag applies, and the same wall only takes 4 bags of it.
That's a near-fivefold difference in bags per square foot between the two products on the same wall, and it's why ordering 'enough stucco' as one line item goes wrong — a supplier needs to know you want 19 bags of one product and 4 of a completely different one. The 15 lath sheets this system also needs are a separate order again, since lath has nothing to do with either coat's coverage rate.
A 40 by 8 foot two-coat wall over concrete block, no lath
| Wall length | 40 ft |
|---|---|
| Wall height | 8 ft |
| Opening area | 0 sq ft |
| System | Two-coat over masonry |
| Scratch coat | 0.375 in |
| Brown coat | 0.5 in |
| Finish coat | 0.125 in |
| Waste factor | 10 % |
| Base coat bags | 18 80 lb bags |
|---|---|
| Finish coat bags | 6 80 lb bags |
| Stucco area | 320 sq ft |
| Base coat thickness | 0.5 in |
| Base coverage per bag | 20.3 sq ft |
| Lath sheets | 0 sheets |
| Total applied volume | 16.7 cu ft |
This wall is bigger (320 square feet, no openings) and the brown coat is troweled thicker at 1/2 inch, yet it takes about the same base coat bag count as the smaller three-coat wall — 18 against 19 — because a two-coat system only pays for one base layer instead of two. Notice the scratch coat thickness field is still set here at its default 0.375 inch, but it never enters this calculation at all: a two-coat system over solid concrete block has no scratch coat, so that input is simply unused for system 1.
Finish coat bags come out higher than the first example (6 against 4) purely because this wall has more area and no openings to deduct — the finish coverage rate itself hasn't changed. Zero lath sheets show up here, which is correct and not an omission: this system bonds directly to the block, and ordering lath for it would be ordering material with nothing to nail it to.
Common mistakes
- Treating 'stucco coverage' as a single number that applies to both base and finish coat. They're different products with different reference thicknesses, and using one bag count for both under-orders whichever coat wasn't the reference.
- Forgetting coverage scales inversely with thickness. A brown coat troweled twice as thick doesn't need twice the bags per the same rate — it needs a rate that's been halved, which changes the bag count by more than doubling the thickness alone suggests.
- Entering only the brown coat thickness on a three-coat job and leaving the scratch coat's contribution out of the base thickness total. The two coats stack, and the bag count depends on their combined depth.
- Ordering lath for a two-coat system bonded directly to masonry, or skipping it on a three-coat system over open framing. Lath exists to give the base coat something to key into on framing; solid masonry doesn't need it.
- Running the bag count against gross wall area on a wall with a lot of glazing. A large window or sliding door wall can lose 20% or more of its area to openings, and that comes off before either coat's coverage is applied.
- Assuming the finish coat can go on heavier than its reference thickness to save a coat or hide substrate irregularities. Texture, crack resistance, and coverage move together with finish coat depth — applying it thick changes all three, not just how far the bag goes.
Shopping summary
Order base coat and finish coat as two separate products, in the bag counts this page gives for each — they are not interchangeable and a supplier pricing 'enough stucco' as one figure will get the split wrong. For a three-coat system, lath is a third order again, alongside the fasteners it's attached with.
If the substrate is framed rather than masonry, the lath goes over sheathing, and the sheathing calculator covers that layer and its own fastening schedule — stucco lath fastening is a separate spec from sheathing nailing, but the panel count underneath is worth having settled first. For a two-coat system, confirm the concrete block or masonry wall beneath is sound and clean enough to bond to before ordering base coat at all; stucco applied over a compromised substrate is a callback waiting to happen.
FAQ
Why does the finish coat need so many fewer bags than the base coat?
Because it's applied much thinner — typically 1/8 inch against a base coat that might be twice or three times that combined — and its reference coverage of 70 sq ft per bag is already set for that thin application. It isn't that finish coat 'goes further' as a material; it's a thinner layer of a different product measured against its own reference.
Does the scratch coat thickness matter separately from the brown coat, or can I just enter a combined number?
Enter them separately if you're running a three-coat system — the calculator adds scratch and brown together to get the base thickness that drives coverage, so the split between the two doesn't change the bag total, but leaving scratch at zero when you're actually applying one will understate your base thickness and overstate how far your bags go.
What about a one-coat or synthetic (EIFS) stucco system?
This page covers traditional three-coat-over-lath and two-coat-over-masonry portland cement systems, which is where the published coverage figures above come from. A one-coat or EIFS system uses different base materials with different manufacturer coverage rates, and running those products through these figures would misstate the bag count — check the specific product's data sheet instead.
How much does lath actually add to a three-coat job?
It's a real cost, not a rounding error — a wall needing 19 bags of base coat in the first worked example above also needs 15 sheets of lath, each requiring its own fastening. Skipping it from your budget because it's 'just the backing' is a common way three-coat jobs come in over the material estimate.
Can I use this to figure a small patch repair rather than a full wall?
The coverage math holds at any area, but the practical minimum on a real job is closer to one bag of each product than to a fraction of one — suppliers don't sell partial bags, and a very small patch will round up to a full bag of base and a full bag of finish regardless of how little the arithmetic says you need.
Does the 10% waste figure cover overspray from a hopper gun?
It's a reasonable working default for hand application; a hopper or pump rig can lose noticeably more to overspray depending on wind and operator experience, so raise the waste percentage toward 15% if the finish coat is being sprayed rather than troweled.
Where to go next
The projects this number is a step of, the guides that explain the method behind it, and the rest of its trade group.