Give the slab size, the spacing and the cover, and this returns how many bars run each way, exactly where they sit, the total linear metres once laps are added, and how many ties you will get through.
The requested spacing is a maximum, measured centre to centre. Subtract twice the edge-to-centre distance from the perpendicular slab dimension. Divide that span by the maximum spacing, round UP to get the number of intervals, then add one bar. Actual spacing is the span divided by the number of intervals.
With bar centrelines 50 mm from each edge and maximum spacing of 200 mm, the spans are 5,900 mm and 3,900 mm. The 3,900 mm span needs ceil(3900 / 200) + 1 = 21 bars along the length, at 195 mm centres. The other direction needs 31 bars at 196.7 mm centres. That is 52 bars, 244.8 m of steel before any laps, and 651 crossings for a single two-way grid.
The input is the distance from the slab edge to the BAR CENTRELINE, not clear concrete cover to the steel surface. If your drawing specifies clear cover, add half the bar diameter to obtain this centreline distance. Confirm the layout and cover with your designer.
Bars longer than the stock length have to overlap, and the lap is usually expressed as a number of bar diameters. Set it from your own specification — the default here is a common figure, not a rule.
Stock quantities are conservative: each direction is cut separately and offcuts are not shared between directions or spliced runs. For a spliced run, each extra stock piece adds stock length minus one lap to the covered distance. The tie figure is one tie per crossing for one grid; it is not a tying specification and does not include extra layers or chairs.
It does not size reinforcement. Bar diameter, spacing and layer position are structural decisions that depend on loads and ground conditions — this tool lays out what you were told to place.
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