Revit Reference Plane and Reference Line: Differences and How to Use Them

A Revit reference plane is a green dashed guide used to sketch geometry, host elements and lock dimensions. A reference line is a solid guide available only while building families: in the Family Editor or with Model In-Place. According to Autodesk, reference lines are rotatable and reference planes are not (Autodesk: Add a Reference Line).

This article compares the two, then works in Revit 2027 through drawing, naming, the Is Reference and Defines Origin properties, EQ dimensions driven by a parameter, the four work planes of a reference line and angle parameters. To learn family building properly, see the Revit Family course.

Reference line vs reference plane

The rule: when a straight dimension changes, use a reference plane; when an angle changes, use a reference line. Most families use both.

Drawing reference planes and reference lines

1. In a family, click Create › Datum and choose Reference Plane or Reference Line. A normal project environment has only reference planes, under Architecture › Work Plane › Ref Plane. The shortcut RP draws a reference plane in both.
2. Pick a tool on the Draw panel. Reference planes have Line and Pick Lines; reference lines have every shape plus Chain for connected segments.
3. To offset from a picked edge, type a value in Offset before drawing.
4. Click the start point and the end point. Press Esc twice to finish.

In plan, a reference line is solid and a reference plane is dashed.

Reference plane properties: Is Reference, Defines Origin

Select a plane and Properties shows the following (Autodesk: Reference Plane Properties):

A plane newly drawn in a Revit 2027 family defaults to Weak Reference and does not have Defines Origin ticked.

Is Reference: what a project can dimension to

Is Reference has 12 values. The first three are Not a Reference, Strong Reference and Weak Reference. The other nine are predefined names: Left, Center (Left/Right), Right, Front, Center (Front/Back), Back, Bottom, Center (Elevation), Top.

According to Autodesk:

• Named values and Strong Reference are strong references with the highest priority for dimensioning and snapping. The names only help when authoring families; they all behave the same.
• Weak Reference has a lower priority.
• Not a Reference is ignored by dimensioning and snapping in the project.

Autodesk's example is a door family with 24, 30 and 36 inch types, where the left plane is set to Left in every type. In the project, dimension from a wall to the left side of the 24 inch door, then swap it for the 30 inch door. The dimension is kept, because Revit holds on to the same Left reference.

A reference line has the equivalent field, called Reference, also defaulting to Weak Reference.

Defines Origin: the family insertion point

The intersection of two planes with Defines Origin is where the cursor rests when placing the family (Autodesk: Define the Family Origin). Templates usually set it on the two centre planes.

To change the insertion point:

1. Open a plan of the family. Hold Ctrl and select the two planes that cross at the new insertion point.
2. Click Pin (PN) to pin both planes.
3. With both still selected, tick Defines Origin in Properties.

Autodesk recommends keeping this intersection at the family's internal 0,0 point.

Locking reference planes with EQ and a parameter

This is used in almost every family whose size changes. The example builds a width symmetric about the centre.

1. Draw two vertical reference planes, one left and one right of the centre plane.
2. Type DI. Click the left plane, the centre plane and the right plane in turn, then click in empty space to place the dimension string.
3. Press Esc twice. Select the dimension string and click the EQ symbol above it. Both spaces become equal.
4. Type DI again and dimension from the left plane to the right plane.
5. Select the overall dimension. On the Label Dimension panel, click Create Parameter.
6. Name it, for example Rộng (width), keep Type, and click OK.
7. Open Family Types on the Properties panel, change the value and click Apply to test.

Step 7 is called flexing the family. Do it after every new parameter to catch errors early.

Naming a reference plane to use it as a work plane

1. Select the plane.
2. In Properties, click Name and type a name, for example Mép trái (left edge).
3. Click Apply. Pressing Esc before Apply discards the name.
4. Click Create › Work Plane › Set. The newly named plane is in the Name list.

Unnamed planes do not appear in this list, so name planes as soon as you draw them.

Revit reference line: four work planes

According to Autodesk, when a reference line is selected or highlighted, its associated planes display. A 3D view shows four planes: one horizontal and one vertical running along the line, and one perpendicular plane at each endpoint.

Because a reference line has no Name field, it never appears in the Name list of the Work Plane dialog. To build geometry on one of its planes:

1. Click Create › Work Plane › Set.
2. Choose Pick a plane and click OK.
3. Hover over the reference line. If the wrong plane highlights, press Tab to cycle to another plane, then click.
4. Create geometry, for example an Extrusion, on that plane.

To check which plane a piece of geometry sits on, select it and read Work Plane in Properties, or click Create › Work Plane › Show.

Angle parameter with a reference line and an angular dimension

An angular dimension measures the angle between two lines or planes. Labelling it with a parameter is how you drive a reference line's angle. The example builds a line rotating about the family centre.

1. In the Ref. Level plan, click Create › Datum › Reference Line.
2. Click the start point exactly on the intersection of the two centre planes. Move outwards at an angle and click the end point.
3. Press Esc twice. Type DI, then click Angular on the Dimension panel of the Modify | Place Dimensions tab.
4. Click the horizontal centre plane, click the reference line, then click in empty space to place the arc.
5. Press Esc twice. Select the angular dimension and click Create Parameter on the Label Dimension panel.
6. Name it Góc (angle) and click OK.
7. Open Family Types, change Góc and click Apply to test.

The line rotates about its start point because the start point was drawn exactly on the intersection of the centre planes. In the example, after labelling, Revit redrew the arc on the opposite angle; the value still measures between the same two lines. This technique suits parts that rotate by a typed value: a door leaf opening at an angle, a lamp arm, chairs around a round table.

Locking geometry to the guides

Planes and lines are only a frame. Geometry must be attached to follow them. Autodesk gives three steps:

1. Align a face of the geometry to the reference plane or line with Align (AL): click the guide first, then the face, then click the padlock.
2. Dimension to the guide and label it as a Type or Instance parameter.
3. Flex the family in Family Types, click Apply and check the geometry follows.

The full family workflow is in creating Revit families, with worked examples in the isolated footing family and the lighting fixture family.

Reference planes in a project

In a project, reference planes mark verandah edges, secondary axes or roof ridges, or serve as a plane to host elements. They do not print, but they show in every plan they cross. To keep the screen tidy:

1. Select the planes to hide.
2. Type EH to hide them permanently in the current view, or HH to hide them temporarily.
3. To hide a whole group, give the construction planes one Subcategory and turn it off in Visibility/Graphics.

Assigning scope boxes to planes is covered in scope boxes in Revit.

Common problems

Frequently asked questions

Does a Revit reference plane print?

No. Reference planes only show on screen as guides.

How is a reference plane different from a grid?

A grid has a bubble, prints on drawings and locates the building. A reference plane has no symbol, does not print and serves as a guide and as the skeleton of families.

Can a Revit reference line be used in a project?

Only with Model In-Place, which opens Family Editor tools inside the project. In the normal project environment the guide is Ref Plane on the Work Plane panel. See model in place in Revit.

When should I use a reference line instead of a reference plane?

When a part must rotate with an angle parameter. For straight dimensions, a reference plane is steadier because it is an infinite plane.

Should an angle parameter be Type or Instance?

Type if every instance of a type shares one angle. Instance if each instance in the project needs its own, such as door leaves opened to different angles. Choose it in the Create Parameter step.

In short, the Revit reference plane is the skeleton of families and a guide in projects; the reference line is the rotatable guide used for angle parameters. Right after drawing a plane, name it, set Is Reference, and if it marks the insertion point, tick Defines Origin and pin it.