How do I get the volume of a slab from an IFC?

If the slab carries base quantities, select it and run the takeoff: NetVolume is summed per element. If it does not, pick its top face with the area tool (face mode), give the area its thickness as a height, and the volume is shown on the label and in the export.

How do I calculate a room's air volume for an air-change rate?

Pick the floor face of the room (or trace its outline), then set the clear floor-to-ceiling height as the area's height. The volume in m³ multiplied by the air changes per hour gives the airflow in m³/h.

Is area × height accurate for an excavation?

For a vertical-sided pit or trench on flat ground, yes. For battered sides, sloping ground or a stepped formation, it is an approximation: split the dig into parts of roughly constant depth, or use a terrain model and a dedicated earthworks tool for the final quantity.

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Tools & comparisons · 2026-10-16 · 7 min

Volumes from an IFC Model: Concrete, Screed, Excavation and Room Air Volume

Many volume questions on a project are one area times one height: the screed on a floor, the dig under a pit, the air in a room for an air-change rate. When the model has no quantity for it — or the thing is not modelled at all — tracing the area and giving it a height gets the number in seconds.

Volumes from an IFC Model: Concrete, Screed, Excavation and Room Air Volume — IFC Viewer Online article cover

A surprising number of volume questions on a project have the same shape: an area times a height. How much screed for this floor at 60 mm? How much spoil from a lift pit 1.4 m deep? How many cubic metres of air in this meeting room, to size its ventilation? None of them needs a solid model; they need an honest area and a height somebody chose.

Key takeaways

Get the area: pick a face in one click, or trace the outline point by point.
Select the area and type a height — a thickness, a depth, a clear height. The volume appears on the label, in the list and in the export.
Several extruded areas add up into a total volume at the bottom of the panel.
When the element is modelled and carries quantities, the takeoff's NetVolume is the better number; area × height is for what is not modelled, or not modelled that way.
A volume can carry a requirement too — "at most 2 m³ per pour" — with pass or fail.

Try it: turn an area into a volume

Opens a sample IFC with the Measure panel. Switch to Area, pick a floor face, select the result and type a height under "Height → volume".

Measuring an IFC model with vertex and edge snapping in IFC Viewer Online

Open the interactive IFC viewer

When to measure a volume by hand

If the thing is modelled as an element with base quantities — a slab, a footing, a beam — select it and take off its NetVolume; it is exact and already accounts for openings. Quantity takeoff from an IFC model explains how. Area × height is for everything else:

Layers that are not modelled: screeds, toppings, insulation boards, a gravel bed.
Spaces, when the model has no IfcSpace or its spaces have no volume: room air volume, a plant room, a fire compartment.
Temporary works and earthworks: a pit, a trench, a blinding layer, a backfill.
Checks of a model's own numbers: does a 250 mm slab of 120 m² really hold 30 m³?

Step by step

Open Measure (M) and choose Area. Face mode measures a whole planar face in one click — the top of a slab, the floor of a room. Points mode traces any outline, closing on the first point.
Select the area in the list. Under its breakdown, type the height in "Height → volume", in the unit you display.
Read the volume on the label in the model and in the list. Rename the item ("Screed L2 — 60 mm") so the export is self-explanatory.
Repeat for each part. With two or more extruded areas the panel shows the total volume.
Copy or export the CSV: it has a Volume column next to the area and perimeter.

Three worked examples

Question	Area	Height	Volume
Screed on a 118 m² floor at 60 mm	118 m² (floor face)	0.06 m	7.08 m³
Lift pit 2.4 × 2.6 m, 1.4 m deep	6.24 m² (traced)	1.4 m	8.74 m³
Meeting room for 6 air changes per hour	32 m² (floor face)	2.7 m clear	86.4 m³ → 518 m³/h

The last line is the reason MEP engineers ask for room volumes: airflow is volume times air changes per hour. Use the clear height (floor to ceiling), not the storey height, or the airflow is oversized by the depth of the ceiling void.

Where area × height stops being honest

Sloping ground or a sloping formation — the depth is not one number. Split the area into parts of similar depth.
Battered excavation sides — the top is larger than the bottom. Average the two areas (a prismoid) or use an earthworks tool.
Non-planar outlines — if the traced points are not on one plane, the panel says the area is projected; the volume inherits that.
Concrete orders — add waste, over-break and the volume of reinforcement as your practice does. The model gives the net figure.

Volumes from an IFC Model: Concrete, Screed, Excavation and Room Air Volume