Stucco and plaster calculator

This stucco calculator estimates material coat by coat instead of giving one rough number. Enter the area, choose the layers, and for each one you get the weight and the number of whole bags.

• 3-coat stucco: scratch, brown and finish coats, the traditional system over lath.
• 2-coat stucco over CMU or concrete: the masonry provides the bond, so there is no scratch coat.
• Interior plaster (it works as a plaster calculator too): base coat, skim coat, textured finish coat and primer.

The materials list adds corner bead, with editable unit prices and an estimated total. Every consumption rate and allowance is visible and can be changed. It starts in US units and switches to metric with one click, needs no sign-up, and runs entirely in your browser. Export the result to PDF or Excel for free.

For each coat:

1. Pounds per sq ft = consumption (lb per sq ft per inch of thickness) × coat thickness (in). Thin finishes and primers are usually given straight in lb per sq ft.
2. Material (lb) = area × pounds per sq ft × (1 + waste %).
3. Bags = material ÷ bag weight, rounded up.

Most bags state a yield rather than a consumption rate. Convert it: consumption per sq ft per inch = bag weight ÷ yield in cu ft ÷ 12. An 80 lb bag that yields 0.8 cu ft gives 100 lb per cu ft, or 8.33 lb per sq ft per inch (about 1.6 kg/m² per mm).

Waste covers mortar left in the mixer and on the hawk and material that falls off the wall. 5% is a sensible minimum; rough or out-of-plumb walls need more because the real average thickness is higher.

Assume an exterior wall area of 300 sq ft (27.9 m²), a base-coat mix in 80 lb bags yielding 0.8 cu ft (8.33 lb per sq ft per inch) and 5% waste.

That is about 2,300 lb of material for a 7/8 in system. The finish coat is often a different product with its own yield, so enter its own numbers. On CMU or concrete, delete the scratch coat and calculate the brown and finish coats only.

Metal lath, building paper and weep screed are not part of this estimate; price them separately for a framed wall.

• Scratch coat: pressed into the lath and scored horizontally so the next coat can grip. Needed over wood framing with lath.
• Brown coat: builds the wall flat and true. It is the coat most affected by uneven walls.
• Finish coat: gives color and texture. Its thickness follows the texture or aggregate size, so coarse finishes use more material per square foot.
• Interior base plaster and skim coat: gypsum-based plasters are for dry interior rooms only. A skim coat is a thin smoothing layer, often applied in two passes.
• Primer: goes under textured finishes and paint, and is calculated per square foot without a thickness.

Curing and waiting times between coats come from the manufacturer and your local code. Check the bag or the technical data sheet before you schedule the next coat.

• Using the nominal thickness on a wavy wall. Measure how far the wall is out of plane and use the real average thickness.
• Mixing up lb per sq ft and lb per sq ft per inch. Base coats are rated per inch of thickness; finishes and primers per square foot.
• Forgetting corner bead. Every outside corner and window return needs it; it is a separate line in the materials list.
• Rounding at the end instead of per coat. Bags of different products are not interchangeable, so the tool rounds each coat separately.
• Putting gypsum plaster in wet areas. Bathrooms, basements and exterior walls need cement-based products.