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Joist and hollow-block floor calculator

Enter the span (along the joists) and the width of the floor, then the joist spacing, the bearing and the block length from your supplier’s data sheet: PRAXAO counts the joists, the hollow blocks with waste, the welded mesh and the concrete, cement, sand and gravel of the compression topping. It sizes nothing.

Dimensions

m
m

Material

From the supplier’s data sheet: 60 cm is only a starting value.

cm
cm
cm

An assumption for the quantity of concrete, not a structural thickness.

cm
Advanced options
%
%

Enter the dimensions to see the drawing.

Calculation results

Fill in the fields to see the result.

Preliminary estimate from the values entered: not a structural validation and not an execution plan. Check the local rules and the manufacturers’ data.

Your last inputs are kept in this browser.

Results are provided for information. Check tax rates and legal requirements that apply to you.

How to use it

  1. Enter the span along the joists and the width across them, in metres.
  2. Enter the joist spacing, the bearing on the supports and the block length from the supplier’s data sheet.
  3. Enter the topping thickness you were given and the waste percentages.
  4. Read the joists, the blocks to buy, the mesh and the topping materials.

Examples

4 m × 3 m floor, 60 cm spacing, 10 cm bearing, 20 cm blocks, 5 cm topping

6 joists of 4.20 m (25.20 m), 5 rows of 20 blocks: 100, i.e. 103 with 3 % waste; 13.20 m² of mesh and 0.60 m³ of topping before waste.

Frequently asked questions

Does it design the floor?

No. It counts what a set of dimensions requires. Joist type, spacing, bearing, block height and topping thickness come from the supplier’s data sheet and the engineer’s drawings; the tool never proposes them.

Why is there an alert above 5 m?

It is only a PRAXAO alert threshold to remind you that a large span needs an engineer’s check. It is not a rule and not a validation.

What is not counted?

Props, tie beams, edge reinforcement, bars over supports, openings and trimmers. Follow the drawings and the supplier’s installation guide.

Guides to go further

BUILNORA

Concrete Calculator

Volume of concrete for slabs, footings and columns, with waste margin and cement, sand and gravel quantities.

BUILNORA

Rebar Weight Calculator

Weight of reinforcing steel from diameter and length, laps included, and the 12 m bars to buy.