Floor Screed (Floor Mud) Calculator

Floor mud for a shower pan is a small bay with a slope, not the whole bathroom floor. Measure the pan as its own rectangle, then the rest of the bathroom as a second run, and add the volumes. A pre-slope under a membrane is often thinner than the mud bed over it. The 50 mm starting depth is a bonded-layer starting point, so lower it for a pre-slope and raise it only when the specification says so. The bag count uses 11.6 litres, the yield QUIKRETE states for a 50 lb Deck Mud bag.

Floor mud and floor screed are the names people type when they need the wet volume of a floor layer, not a shopping price. This page stays on that volume. Measure to the edges of the bay that will be filled. If a doorway is also being brought up to the same level, include that threshold as its own small rectangle rather than stretching the room length past the frame. Thickness is the depth you intend to place, in millimetres, so 50 in the field means 50 mm and 0.05 m in the multiplication. Read the specification before you trust the starting value. A bonded screed stuck to a prepared slab, a unbonded sheet, and a floating screed on insulation are specified at different depths, and a pumpable flowing screed is sold by a different yield than a site-mixed sand-and-cement batch. The calculator cannot see which one you are placing.

Waste is a percentage you choose. Ten percent on 0.40 cubic metres adds 0.04 cubic metres. That allowance is for spillage, a hollow that runs deep, and what sticks in the tub. It is not a second copy of the room. If the slab below is out of level by more than the screed can honestly fill, fix the slab or divide the bay, because a single thickness cannot describe a wedge. The bag line is ceiling division of the wasted volume by the litres you type. A 20 litre bag in 0.44 cubic metres is 22 bags because 0.44 divided by 0.02 is 22. If your bag says 25 litres, type 25 and the count changes. Leaving the field at 0 keeps the count at 0 so the page never invents a brand. The kilogram line is the same idea for weight: type the fresh density your plant quotes, or leave it at 0. A metric tonne is 1,000 kg. This page does not convert that weight into a short ton and does not turn it into money.

Order from the volume with waste, then ask the supplier how they sell it. Some merchants sell pre-blended bags. Some sell damp sand and cement separately, and the kilograms-per-cubic-metre field is only useful if they gave you a density. Some send a truck of flowing screed billed by the cubic metre. In that last case you can ignore bags and kilograms and read the cubic metres directly. Tell them the figure is an estimate from your measurements. Check the bay once more on site after demolition, because a plan dimension and a taped dimension often disagree by a few centimetres, and a few centimetres across a wide room is a visible slice of volume. If you are about to tile the screed, the tile calculator counts tiles and the grout calculator counts joint volume. Neither of those replaces this volume.

A worked bay makes the arithmetic easy to audit. Length 5 m, width 4 m, thickness 40 mm is 5 × 4 × 0.04 = 0.80 cubic metres. At 5% waste the order volume is 0.84 cubic metres. A bag that yields 18 litres is 0.018 cubic metres, and 0.84 divided by 0.018 is 46.67, which rounds up to 47 bags. If you do not know the yield, stop at 0.84 cubic metres and let the supplier convert it. Do not type a guessed yield just to see a bag count, because a wrong yield scales every bag. The same discipline applies when only part of the floor is being levelled: measure that patch, not the whole room. After the screed is down, coverage for paint or tile starts from the finished area, which is length times width and does not depend on the thickness you just poured.

Length starts at 4 m. Bay length in metres. Switch to ft / in for feet. Width starts at 3 m. Bay width in metres. Switch to ft / in for feet. Thickness starts at 50 mm. Screed thickness in millimetres, or inches on the ft / in toggle. Waste allowance starts at 10 %. Covers spillage, a slightly deeper patch, and the material left in the mixer. It does not cover a second room. Litres per bag starts at 11.6 L. 11.6 L is the 0.41 cu ft yield QUIKRETE states for a 50 lb Deck Mud bag on the Home Depot listing checked 27 October 2026. Edit it for a different bag. Kilograms per cubic metre starts at 1950 kg/m³. 1,950 kg/m³ is about 122 lb/ft³, the 50 lb QUIKRETE Deck Mud bag divided by its cited 0.41 cu ft yield. A different mix has a different density.