Geometry & modeling
Parametric modeling
Definition
Parametric modeling builds a CAD model from dimensions, constraints, and an ordered list of features, so changing a value regenerates the geometry. It is the default approach in SolidWorks, Fusion, Onshape, Creo, NX, and FreeCAD Part Design.
Also known as: parametric CAD, history-based modeling, parametric design
Updated
How it works#
A typical parametric part starts as a 2D sketch. Dimensions and geometric constraints fix the sketch's size and shape. Features such as extrude, revolve, cut, fillet, and pattern then turn sketches into solid geometry, each one building on the result of the last.
The software records every step. In Onshape, a Part Studio contains the Feature toolbar, the Feature list, and the graphics area, and the model is the result of running that list in order. Change a dimension in an early sketch and every later feature recalculates.
What parameters buy you#
The main benefit is controlled change. A bracket built with its hole spacing as a driving dimension can be resized without redrawing it. Families of parts can come from one model with different parameter values. A well-built model captures design intent: which features stay centered, which edges stay tangent, and what moves when something changes.
Where it breaks#
Parametric models depend on references. A feature attached to a face or edge created earlier can lose that reference when an upstream change removes or renames the geometry. The result is the familiar red error in the history. Deep feature trees also get slow to rebuild and hard for another person to understand.
For those reasons many tools now mix approaches. Shapr3D, for example, says it integrates direct and history-based workflows, and most parametric programs include direct editing tools for imported geometry.
Parametric output and AI#
Most text-to-CAD tools in 2026 output exact geometry without a usable feature history. A STEP file from an AI tool is not parametric in the sense above: it has no sketches, constraints, or driving dimensions. Tools that write CAD code, such as OpenSCAD or CadQuery scripts, or that drive a CAD program's API, can produce models with editable parameters, but only as well as the generated code is structured.
Sources
Related terms
Feature tree
A feature tree is the ordered list of operations, such as sketches, extrudes, cuts, fillets, and patterns, that builds a parametric CAD model. Editing an early feature replays every feature after it, which makes controlled changes possible and also makes the model depend on each earlier step.
Sketch constraint
A sketch constraint is a rule applied to 2D sketch geometry, such as coincident, parallel, tangent, equal, or a fixed dimension. When a sketch is fully constrained, nothing in it can move freely, which makes later edits predictable.
Design intent
Design intent is the reasoning built into a model's structure: which dimensions drive others, what stays centered or symmetric, and what should move when something changes. Two models that look identical can behave very differently when edited because of how their intent was captured.
Direct modeling
Direct modeling edits geometry by pushing, pulling, moving, and deleting faces directly, without replaying a feature history. It is fast for imported files and late changes, but it does not record why the model has its shape.