Stucco & Plaster Calculator
Stucco or plaster by coat: the volume of each coat at your thickness, the bags or the sand and cement it takes, plus lath sheets and corner bead.
Net area after openings, the volume and bag count of every coat at your thicknesses, the total with waste and what it costs, or sand and cement by your mix ratio, with lath sheets and bead sticks.
Example: 800 sq ft less 60 sq ft of openings in three coats at 3/8, 3/8 and 1/8 in comes to 1.68 yd³ with waste — 17 bags at 45 sq ft per bag per inch, $306 at $18 a bag.
Area times thickness,
one coat at a time.
Why each coat is counted separately, where the bag and mix figures come from, and what is deliberately not stored.
Coat by coat
Render is bought by volume, not by area, so each coat is worked out on its own: net area × that coat’s thickness. A three-coat system is scratch, brown and finish; two-coat is a thicker base and a finish; one-coat is a single pass. Openings come off the gross area once, and the waste allowance is applied to the total at the end rather than to each coat, which is how the material actually gets wasted — in the mixer and on the ground, not per layer.
Bags or site mix
A bagged mix is counted from the yield printed on your bag: coverage at one inch (or ten millimetres) scales inversely with the thickness you apply, and the bag count is rounded up per coat because you cannot buy part of a bag. A site mix is counted by volume instead: sand and cement in the ratio you set, multiplied by a dry-volume factor because loose materials lose volume when they are combined and wetted. Both the yield and the factor are yours from the product data sheet.
Limits
No code minimum thickness, no fire rating, no weather-resistive barrier requirement and no product table: coat thicknesses, bag yields, mix ratios and prices are all your inputs, because they differ between products and between a wall, a ceiling and a soffit. Lath and bead are counted as whole sheets and sticks with no allowance for the pattern of cuts on your elevation. Nothing leaves the browser; the same four anonymous usage counts as the rest of the site apply.
SOURCES
- Volume = net area × coat thickness plus your waste allowance; bag yield, coat thicknesses, mix ratio and dry-volume factor are yours from the data sheet; no code minimum thickness is applied
Last reviewed 22 September 2026. How results are checked: How we verify.