Centering poles calculator

Here is the calculator run on three common slab sizes. Each row uses the same rule: one prop at every gap along each side, one extra row for the edges, then the extra percentage on top.

The 1,000 sq ft slab needs about four times the poles of the 300 sq ft slab, even though it is only a little over three times the area. A closer gap adds rows in both directions, so the count climbs fast.

• Gap between props. This moves the count the most. On a 40 x 25 ft slab, a 3 ft gap needs 150 props and a 2.5 ft gap needs 187.
• Slab thickness and beams. Thicker slabs and beams carry more wet concrete, so engineers often ask for a closer gap and extra props under the beams. Count beam props separately and add them to the total.
• Breakage and reuse. Poles are reused slab after slab, and a few crack, bend or get cut short each time. That is what the extra percentage covers. Use a higher figure if the same poles will go through many floors.
• Openings. Staircase openings and ducts need fewer props. You can subtract them, but counting the full rectangle leaves you spare poles for edges and beams.

The calculator tells you how many poles to order. Length and thickness decide which poles.

• Length. Take the clear height from the floor to the underside of the slab, then add what your contractor needs for wedges or base plates. Our poles run from 10 ft to 30 ft, so tell us the length for each floor if your floor heights differ.
• Thickness. Measured at the bottom end of the pole. Props under a wet slab need thicker poles than fencing or shade nets. Your engineer gives the minimum size.
• Straight, sound poles. A prop should stand straight and have no deep splits. Ask us on WhatsApp for photos of your lot before the lorry leaves.

For more on sizes, read the eucalyptus pole sizes guide or see eucalyptus poles for centering.