Understanding your result
The headline is the bags of screed mix, with the volume, depth and weight beneath it. The table gives the area, depth, volume with the allowance, the bag, the bag count, the weight to carry and the ready-mix alternative.
Volume is the area times the average depth, plus an allowance for a base that is not perfectly flat; 10% suits a reasonable slab, and a floor with dips or falls to a drain may need more. Bags come from the yield of the bag you choose, which is the volume of mixed screed one bag makes, not its weight. An 80 lb bag of sand-cement mix yields roughly 0.6 cu ft; check the yield table on your product.
Weight is the reason to look twice. Two inches of screed over a small room is well over a ton of bags to carry and mix. When the bag count passes about forty, the note suggests ready-mix or a proper mixer. For a thin correction, the self-leveling compound calculator is the better tool; for the membrane under an unbonded screed, the moisture barrier calculator; and for what the floor will carry, the flooring weight calculator.
How we calculate this
Bag yields are from manufacturer yield tables for sand-cement floor mixes and are approximate; dry-pack and semi-dry screeds yield slightly less per bag than wetter mixes. The depth is the average over the floor, so for a screed laid to a fall, use the average of the deep and shallow ends. The self-leveling guide compares screed and leveler, and the radiant heating guide covers screeds over heating pipes, which have their own minimum cover.
The assumptions behind the numbers
| Assumption | Default | Where it comes from |
|---|---|---|
| Bag yield | 80 lb ≈ 0.6 cu ft, 60 lb ≈ 0.45 cu ft; 25 kg ≈ 12.5 L | Manufacturer yield tables for sand-cement mixes (for example Quikrete) |
| Depth | 2 in (50 mm) | Typical unbonded screed; bonded screeds are thinner |
| Allowance | 10% | Uneven base and mixing losses |
| Minimum depth | about 1 in (25 mm) for sand-cement | Common practice; thinner screeds crack and curl |
| Drying | about 1 mm per day for the first 40 mm | Common rule of thumb for sand-cement screeds; test before flooring |
Assumptions last reviewed October 8, 2026.
The calculator does not mix-design a screed or choose between sand-cement, anhydrite and fast-drying proprietary screeds, which have their own yields and drying times. It does not count the edge strip, the membrane or the reinforcing mesh a floating screed may need, and it does not judge whether the floor below can carry the weight; on a timber floor upstairs that is a question for a structural engineer.
Two worked examples
A 15 × 12 ft utility room at 1 1/2 in
80 lb bags, 10% allowance.
- Volume: 180 × 1.5 ÷ 12 = 22.5 cu ft; with 10%: 24.8 cu ft (0.92 cu yd)
- Bags: 24.8 ÷ 0.6 = 41.3, rounded up to 42 bags
- Weight: 42 × 80 lb = 3,360 lb, 1.68 tons
Forty-two bags is at the point where a mixer and two people are the minimum, and where a ready-mix order of just under a cubic yard becomes worth pricing.
A 60 sq ft shower area at 3 in average
Laid to a fall, 60 lb bags.
- Volume: 60 × 3 ÷ 12 = 15 cu ft; with 10%: 16.5 cu ft
- Bags: 16.5 ÷ 0.45 = 36.7, rounded up to 37 bags
- Weight: 37 × 60 lb = 2,220 lb, 1.11 tons
A sloped bed is deep at the walls and shallow at the drain, so the average depth matters; using the deepest point would have bought half again as many bags.
Where to find your inputs
Area. Wall to wall, the whole area being screeded.
Depth. Measure from a level line to the slab at several points and average them; for a fall, average the high and low ends.
Bag. The yield is in the product’s data, in cubic feet or litres per bag.
Allowance. 10% for a reasonable base; more for a rough or dished slab.
Common mistakes
- Using the bag weight as its volume. Bags are bought by weight but cover by yield.
- The deepest point as the depth. Use the average.
- A screed too thin. Under about 1 in, sand-cement cracks; use a leveler.
- Laying flooring on a wet screed. Test the moisture; days are only a guide.
- Forgetting the weight. A ton of bags needs a plan to get it in.
- Hand-mixing a big floor. Over a cubic yard, order ready-mix or rent a mixer.
Questions people ask
- How much screed do I need for a 12 × 10 floor?
- At 2 inches deep, 120 sq ft × 2/12 = 20 cu ft, or 22 cu ft with 10% for an uneven base. In 80 lb bags yielding about 0.6 cu ft each that is 37 bags, close to 1.5 tons. In ready-mix it is 0.81 cu yd.
- How thick should a floor screed be?
- A screed bonded to the slab is usually 1 to 1 1/2 inches (25 to 40 mm); an unbonded screed over a membrane at least 2 inches (50 mm); a floating screed over insulation at least 2 1/2 to 3 inches (65 to 75 mm). Thinner sand-cement screeds crack and curl.
- How long does screed take to dry?
- The common rule of thumb for sand-cement screed is about 1 mm a day for the first 40 mm and slower beyond, so a 50 mm screed may need two months before moisture-sensitive flooring. Test the moisture rather than counting days.
- How much does a bag of screed cover?
- An 80 lb bag of sand-cement mix yields about 0.6 cu ft, which covers about 3.6 sq ft at 2 inches or 4.8 sq ft at 1 1/2 inches. A 25 kg bag yields about 12.5 litres, about 0.25 m² at 50 mm.
- Should I use screed or self-leveler?
- Self-leveler for thin corrections up to about an inch, where it flows flat on its own; screed for deeper build-ups, falls to a drain and floors over heating pipes. Screed is cheaper per cubic foot but needs skill to rule flat.
- When should I order ready-mix screed instead?
- Above about a cubic yard (0.75 m³), mixing by hand is slow and inconsistent. Pumped ready-mix or a forced-action mixer gives a better screed and saves a day of labour.