How to measure a concrete slab from drawings
Quick answer
Measure the slab area on the plan, then multiply by the slab thickness to get volume (m³). Add thickenings, downstands or edge beams separately, apply waste, and export. You can measure the area free in the browser and do the volume maths from the total.
Concrete is priced by volume (m³), but drawings give you area and a thickness note. So slab take-off is: measure the area accurately, then multiply by thickness — plus any thickenings.
Here's a clean way to do it and keep it checkable.
Step by step
- 1
Set the scale
Calibrate the sheet with a preset ratio or by drawing a known dimension.
- 2
Measure the slab area
Trace the slab outline with the area tool to get the plan area in m². For pours in sections, measure each bay separately.
- 3
Note the thickness
Read the slab thickness from the section or the general notes (e.g. 150 mm = 0.15 m).
- 4
Calculate volume
Volume = area × thickness. For a 120 m² slab at 0.15 m, that's 18 m³. If bays differ in thickness, calculate each and sum.
- 5
Add edges, thickenings and beams
Measure edge thickenings, downstand beams or toes as separate items (area × depth, or cross-section × length) and add them to the total.
- 6
Apply waste and export
Add a waste/over-order allowance (spillage, levels), then export the areas to CSV and record thicknesses so the volume is auditable.
Tips & gotchas
- •Concrete is sold by volume — always convert area × thickness to m³.
- •Read thickness from the section, not the plan; watch for different thicknesses per bay.
- •Measure edge beams and thickenings separately — they add real volume.
- •Add a sensible over-order allowance; you can't un-pour a short load.
Frequently asked questions
How do I calculate concrete volume from a plan?
Measure the slab area on the plan, then multiply by the slab thickness (from the section). Area 120 m² × 0.15 m = 18 m³. Add thickenings and beams separately.
The drawing only shows area — where's the thickness?
Thickness is usually on the section drawing or in the general/structural notes, not the plan. Use that figure for the volume calculation.
How do I handle edge beams and thickenings?
Measure them as separate items (cross-section × length, or extra depth × area) and add to the slab volume so nothing is missed.
Can I measure the area for free?
Yes — area measurement and export are on Solid Takeoff's free plan; do the area × thickness step from the totals.
Try it on your own plan — free
Open a PDF and measure in your browser. No card, no install, no CAD. Free plan forever.