We’re often asked this. Clients want to purchase enough, but not more than necessary. After all there’s the purchase cost, and then the transport cost to consider. Having just enough to finish the installation is so satisfying, but falling short is no joke and can add a huge cost to the project, and delay it, particularly when the shipping was to a distant land ! Paying that extra cost, and the long wait can turn a good choice into a regrettable dilemma. Rest assured that BCA’s staff are used to assessing the surface areas and weights, and tend to add some to play safe. After all we sell them per square meter (1m2 = 10.76 sq ft) rather than per cobble or sett, or per tonne.
Nevertheless loading stone into big bags on site is NOT an exact science. If it was an exact science the measurement of each stone x the number of stones would bump up the sale price unacceptably.
This is particularly true as reclaimed materials are rarely cubes, and have size differences and irregularities which are part of their charm and authenticity.
It’s different for new industrially-processed calibrated paving with uniformity, as their machinery is set up for exactitude. Therefore please over-order very slightly, and perhaps have in mind a zone where you could use the excess if there is any.
That also allows you to select out any that you feel are less attractive for any reason (colour, weird size, too worn ….. etc), although generally that’s not necessary.
This also relieves pressure on your builders undertaking the installation, as some can be negative and irritated about using antique reclaimed materials requiring more care to install than new paving. Assuring your team that there are plenty is good practice, and after all they may have justifiable concerns if they’ve had issues on previous projects less well planned.
Concerning how many cobbles are in a square meter : Clearly a cube format close to 10cm x 10cm x ht 10cm (4 x 4 x ht 4 inches) will require approx. 100 per sq meter (or approx. 9.3 per sq ft).
However the question concerns more the antique reclaimed cobbles and setts with varied much bigger sizes that were installed in rows, often of different widths.
Therefore the question is understandably asked more for evaluating the esthetics and suitability of them in the context of the project’s design, with architects and designers clearly needing to appreciate how they’ll look in-situ in order to make the best choice. They’ll also need to draw them onto plans and integrate them in 3D visuals at the correct scale.