Calculate stucco coverage: bags of scratch, brown, and finish coat for any wall area, the area your bags will cover, and total mixing water needed.
Stucco Coverage Formula
The calculator first finds the net wall area, then converts that area into 80 lb bags for each coat:
A = (L * H) - O
Bags = (A * (1 + W/100)) / C
In the reverse mode, the same relationship is solved for area instead of bags:
A = Bags * C
Variables:
- A is the net wall area to be stuccoed (square feet)
- L and H are the wall length and height (feet)
- O is the total area of doors, windows, and other openings (square feet)
- W is the waste allowance as a percent (10% is typical)
- C is the coverage of one 80 lb bag at the chosen coat thickness (square feet per bag)
- Bags is the number of 80 lb bags required for that coat
In the default mode you enter the wall size, pick a stucco system, and the tool applies the bag formula once per coat. A 3-coat system runs it for the scratch coat, brown coat, and finish coat; a 2-coat system runs it for one base coat plus the finish; the finish-only mode covers re-coating existing stucco. The calculator also totals the mixing water for the whole job, at about 1.4 gallons per base coat bag and 2 gallons per finish coat bag, and estimates material cost if you open the advanced options and enter bag prices. Switch the solve-for selector to the second mode to work backwards from bags you already have to the area they will cover.
Bag Coverage, Mixing Water, and Curing Schedule
Coverage per bag depends on the coat and its thickness. These figures come from manufacturer data sheets for pre-blended 80 lb stucco bags, which yield about 0.75 cubic feet of wet material each.
| Coat | Thickness | Coverage per 80 lb bag |
|---|---|---|
| Scratch or brown (base) | 3/8 in | 20 to 24 sq ft |
| Base coat | 1/2 in | 15 to 18 sq ft |
| Base coat | 3/4 in | 10 to 12 sq ft |
| Finish coat, smooth or sand float | 1/8 in | about 70 sq ft |
| Finish coat, lace, dash, or heavy texture | 3/16 in | about 48 sq ft |
Bag counts are only half of the planning. The table below covers the water you need on site to mix each coat and how long each coat must cure before the next one goes on. Running out of clean mixing water mid-wall causes cold joints and color variation, so total it up before you start.
| Coat | Mixing water per 80 lb bag | Cure before next step |
|---|---|---|
| Scratch coat | about 5.5 qt (1.4 gal) | Moist cure 24 to 48 hours |
| Brown coat | about 5.5 qt (1.4 gal) | 7 days minimum before finish |
| Finish coat | about 2 gal | Mist twice daily for 3 to 5 days |
Mix only what you can apply in about one hour, and do not re-temper stucco that has started to set. In hot or windy weather, plan on extra misting water beyond the mixing totals above.
Example Problems
Example 1: 3-coat stucco on a framed wall. You are stuccoing a wall 40 feet long and 9 feet tall with one door and several windows totaling 40 square feet of openings. Net area is 40 * 9 – 40 = 320 square feet. With a 10% waste allowance you need to cover 352 square feet. At 22 square feet per bag for a 3/8 inch coat, the scratch coat takes 352 / 22 = 16 bags, and the brown coat takes another 16 bags. A smooth finish at 70 square feet per bag takes 352 / 70 = 5.03, rounded up to 6 bags. That is 38 bags total, and about 32 * 1.4 + 6 * 2 = 56.8 gallons of mixing water for the whole job.
Example 2: coverage from bags on hand. You have 10 bags of 80 lb base coat left over and want to know how much wall they will cover at 3/8 inch. Area = 10 * 22 = 220 square feet, or about 20.4 square meters. If the substrate is rough or you trowel heavier than 3/8 inch, expect the real number to land closer to the low end of the 20 to 24 square feet per bag range.
Frequently Asked Questions
How many bags of stucco do I need per 100 square feet?
With pre-blended 80 lb bags, plan on about 5 bags per base coat (at 22 square feet per bag and 3/8 inch thickness) and about 1.5 bags of finish coat per 100 square feet. A full 3-coat system therefore runs about 11 to 12 bags per 100 square feet including 10% waste. A 2-coat system over block runs about 6 to 7 bags per 100 square feet.
Why do stucco coverage estimates vary so much between sources?
The biggest reason is bagged mix versus field mix. A pre-blended 80 lb bag already contains the sand, so it yields only about 0.75 cubic feet and covers roughly 22 square feet at 3/8 inch. A field mix made from a bag of plastic cement plus 3 parts sand yields several times more volume per bag of cement, so sources quoting 90 to 110 square feet per bag are describing the cement bag in a field mix, not a pre-blended bag. Check which product a coverage number refers to before you buy, or you can end up with a fraction of the material you need.
Should I use a 2-coat or 3-coat system?
Use 3-coat (scratch, brown, finish, about 7/8 inch total) over wood or steel framing with lath, since the scratch coat is what keys into the lath. Use 2-coat (base plus finish, about 1/2 to 5/8 inch total) directly over concrete, CMU block, or sound existing stucco, where the masonry itself provides the bond and no lath is needed. Going below these thicknesses invites cracking, and going thicker mainly adds cost and weight.
