Quantity takeoff from IFC: estimating is not ordering

The same word, two different meanings

Extracting quantities from a BIM model looks simple: you open the IFC in the right tool and get a table of numbers. In practice, this is where problems start.

The term 'quantity takeoff' means two completely different things. You will also hear material takeoff or bill of quantities; the split below is the same. An estimator tallies a project and draws gross quantities: this building has 500 square meters of facade, 2000 cubic meters of concrete, 1000 windows. A work planner looks at the same numbers and sees something else entirely: how many window frames do I actually order? How many extra fasteners for connections? What if this detail is slightly different? These are not the same calculations. Same spreadsheet, two different worlds.

Estimating versus ordering

Estimation software works with approximate quantities. It adds line items, contingencies, safety margins. The estimator knows the model is not complete reality: details are not modeled, measurements are approximate. So buffer is added. This is useful for a budget estimate. Not for your production lists.

A work planner must order exactly. A forgotten line item means back-order: the part arrives late, production stops, you pay for extra crane and transport, your crew sits idle. A single incident quickly runs into thousands of euros, and it adds up: one wrong line on your order list and the site schedule slips.

Estimation software stops at the takeoff; Koto delivers the lists you actually order and produce with.

What an IFC technically contains for quantities

An IFC contains basic information about objects: a door has width and height, a column has length and profile. Quantities can be derived from this. Base quantities extracted from IFC are: length (for profiles, pipes, rods), area (for sheets, plates, walls, roofs), volume (for concrete, insulation) and count (for discrete items like windows and doors).

Additionally, a Revit or Tekla model may contain property sets with specialized values: material choices, grades, suppliers.

But here the problem begins. The quantities you extract from an IFC depend on how well the BIM model was built and how the CAD packages configured their export settings. Whoever models the window can forget parameters. A Revit parameter may be empty. The IFC itself does not always tell you which values to trust.

Why you need rules above the model

A production-ready quantity takeoff requires more than what sits in the 3D model. You must convert units: IFC works internally in meters, a cutting list works in millimeters, a stack list works in pieces. You need to know which unit applies to each item and convert consistently.

You must account for loss percentages and extras. Saw loss on timber: add three percent, for example. And not everything is modelled: no CAD package models every bolt, every screw, every fastener. A work-preparation system must add those items through rules: per door frame, for example, the hardware and screws from your own standard. Connection pieces and consumables are not in the model and still have to be on the list.

This is where configuration comes in. Configure once, then it runs automatically on every project: you set up once which BIM parameters map to which bill-of-materials columns, which units, which loss factors, which additional rules. Then for every new project you automatically generate a correct quantity takeoff. No more manual copying, no more missed lines.

How it works in practice

You build a pipeline once: you specify which quantities you want from the BIM model, in which units, with which loss factors, with which additional rules. Then you feed each new IFC file and automatically get your production lists: order lists from BIM in Excel, cutting lists, bills of materials, all ready for your ERP. This runs live at prefab manufacturers across the Benelux, who push their projects through it week after week without manual patching.

Frequently asked questions about quantity takeoff from IFC

Which quantities does an IFC contain by default?

Base quantities per element: length, area, volume and count. Whether they are actually in the file depends on the export settings of the CAD package.

Is a quantity takeoff the same as a bill of quantities?

In practice both terms are used for a list of quantities. The real distinction is the purpose: estimating for a price, or ordering for production.

Can I get my takeoff in my own Excel format automatically?

Yes. You define your column format once. Every next export follows that same format, or goes straight to your ERP such as Odoo.

Try it yourself

Test how Koto extracts quantities from your BIM model. Upload your own IFC and see what bill of quantities from IFC emerges. Or schedule a demo to see how this works for your workflow specifically. Request a demo, or try it yourself first.