Drawing a line in Desmos 3D means entering coordinates as a list, not as a single equation

Desmos 3D does not work like the 2D graphing calculator you may have used before. Instead of typing y = 2x + 1, you create a line by giving Desmos a list of points in three-dimensional space. The calculator then connects those points in order, drawing the line between them.

The fastest way is to use a parametric line — a single equation that generates all the points on your line at once. This takes one line of input instead of dozens, and it works whether your line is straight, curved, or anything in between.

Key Takeaways

  • A parametric line in Desmos 3D uses the format (x(t), y(t), z(t)) where t is a variable that moves along the line.
  • For a straight line from point A to point B, use (1-t) * A + t * B with t ranging from 0 to 1.
  • You set the range of t by clicking the three dots next to your equation and choosing domain constraints.
  • Desmos 3D draws the line as you type — you do not need to press Enter or click a button.

The parametric line formula for a straight line

A parametric line uses a variable called t that slides from one number to another. As t moves, the coordinates change, and Desmos plots every point in between.

For a straight line from point A = (x₁, y₁, z₁) to point B = (x₂, y₂, z₂), type this into Desmos 3D:

(1-t)(x₁, y₁, z₁) + t(x₂, y₂, z₂)

Replace x₁, y₁, z₁ with the coordinates of your starting point, and x₂, y₂, z₂ with your ending point. For example, if you want a line from (0, 0, 0) to (3, 4, 5), type:

(1-t)(0, 0, 0) + t(3, 4, 5)

When t = 0, you get the first point. When t = 1, you get the second point. Desmos fills in everything in between.

Setting the range of t so the line stops where you want

By default, Desmos 3D may extend your line beyond the two points you specified. To make the line stop exactly at your endpoints, you need to limit t to the range 0 to 1.

Click the three dots (⋯) to the right of your equation. A menu appears. Select Domain or Restrict domain. Enter 0 in the minimum field and 1 in the maximum field. The line now connects your two points and stops.

If you want the line to extend beyond those points, use a larger range — for example, t from -1 to 2. Negative values of t extend the line backward past your starting point; values above 1 extend it forward past your ending point.

Drawing a curved line or path

You are not limited to straight lines. Any parametric equation works. For example, a helix (a spiral shape) uses the formula:

(cos(t), sin(t), t)

This creates a spiral that winds upward as t increases. Set the domain to something like 0 to 4π to see several complete loops.

The key is that each coordinate — the x, y, and z — must be an equation in terms of t. Desmos evaluates t at many small intervals and plots the resulting points, connecting them into a smooth curve.

Connecting multiple separate line segments

If you need to draw several connected segments — for example, a path that goes from A to B to C — enter each segment as a separate parametric equation. Use the same t range (0 to 1) for each one.

For a path from (0, 0, 0) to (1, 1, 1) to (2, 0, 2), enter two equations:

(1-t)(0, 0, 0) + t(1, 1, 1) (1-t)(1, 1, 1) + t(2, 0, 2)

Each equation is a separate line in the input panel. Desmos draws both, and they meet at the point (1, 1, 1) where the first segment ends and the second begins.

Troubleshooting: the line does not appear

If you type an equation and nothing shows up, check these things first. Make sure your parentheses are balanced — every opening parenthesis must have a closing one. Desmos 3D is strict about this.

Second, check that you are using the correct variable name. Desmos 3D uses t by default for parametric equations, but some versions allow you to choose. If you typed s instead of t, the equation will not work unless you also set s as your parameter.

Third, make sure your domain is set correctly. If you set t to range from 0 to 0.1 and your coordinates use much larger numbers, the line may be too small to see. Expand the domain or zoom out in the 3D view.

Frequently Asked Questions

Can I draw a line between more than two points without entering multiple equations?

Not in a single parametric equation. Each parametric line connects a continuous path. To connect three or more points, enter one equation per segment. If you have many points, you can also paste them as a table and Desmos will connect them, though this method is slower for large datasets.

What if I want the line to be thicker or a different color?

Click the colored circle next to your equation to open the color picker. For line thickness, click the three dots and look for a Style or Line width option. Not all versions of Desmos 3D expose this setting in the same place — check the menu next to your equation.

How do I make a line that goes through specific points but is not straight?

You need a curve that passes through those points. One option is a spline, which Desmos 3D does not build in, but you can approximate one by entering many short line segments. Another option is to use a polynomial or trigonometric function that fits your points, then convert it to parametric form.

Can I connect a line to other objects like surfaces or points?

Yes. Plot your points as separate equations — for example, (0, 0, 0) — and your line as a parametric equation. Desmos draws them all in the same 3D space. You can also layer multiple parametric equations to create more complex shapes.

What does the t variable actually represent?

t is a parameter that controls position along the line. It has no physical meaning on its own — it is just a number that Desmos uses to step through your equation. When t = 0, you are at the start; when t = 1, you are at the end. Values in between give you points along the path.