One slab, two independent material calculations
A 6m by 5m concrete slab needs a compacted gravel base underneath it and a steel reinforcement grid inside it — two different materials, both sized from the same slab footprint but by two unrelated formulas.
The gravel base: 3 m³, 4.95 tonnes
Feeding the real 6m × 5m dimensions into the gravel calculator with a 10cm base depth and a 1650 kg/m³ density gives a real volume of 3 m³ and a weight of 4,950 kg (4.95 tonnes).
The rebar grid: 311m of bar, 491.46 kg
Feeding the identical real 6m × 5m dimensions into the rebar calculator, with 200mm spacing and 16mm bars, gives a real grid of 26 bars lengthwise and 31 widthwise — 311m of total bar length weighing 491.46 kg.
Why sharing the dimensions doesn't mean sharing the formula
Both real results start from the same 6m × 5m footprint, but gravel volume scales with length × width × depth while rebar quantity scales with length and width divided by spacing, plus a diameter-squared weight formula — genuinely different mathematical relationships that happen to take the same two dimensions as a starting point. Changing the slab's spacing or gravel depth moves one material's total without touching the other's calculation at all.