by PaintTool SAI has perspective tools only in Ver.2, and once you know that, the rest is short. Ver.2 has a family of ruler layers, of which the Perspective Ruler with one, two or three vanishing points is the one that matters here. This guide sets it up, snaps strokes to it, and brings in a lens-accurate grid from the tools on this site for the part SAI does not do, which is deciding where the vanishing points should be.
Ver.1 versus Ver.2
SAI Ver.1, the version most tutorials still show, has no rulers of any kind. Everything below is Ver.2, which is Windows-only and has shipped as a technical preview for years while adding features; the ruler set arrived in 2016–2017 and has been refined since. If your layer panel has no ruler options, you are on Ver.1: draw over an imported grid image instead, using the export method at the end.
The rulers
Ver.2's rulers are layers. In the layer panel, the new-layer options include ruler layers, and the Perspective Ruler's own menu on the panel gives access to the related types. The set is: the Perspective Ruler itself (1VP, 2VP or 3VP grids), the Vanishing Point Ruler (a single point that any stroke converges toward, useful for a roof pitch or a stair slope that needs its own point), the Parallel Line Ruler, the Concentric Ellipse Ruler for wheels and cylinder ends, and the Symmetric Ruler. Because they are layers, you can hide them, reorder them, keep several per file and switch between them by selecting a different ruler layer.
Setting up a two-point ruler
Create a Perspective Ruler layer and choose two vanishing points. The ruler draws a horizon and the fans of lines from each point. Drag each vanishing point's control point to where it belongs; for most views both points sit well outside the canvas, so zoom out first. Alt + drag on a control point rotates the ruler; Shift + Ctrl + drag moves the whole thing. Keep the horizon at the height the drawing's eye level should be, which is the one decision the ruler cannot make for you.
For three-point, choose 3VP and place the third point above (looking up) or below (looking down) the horizon on the vertical through the centre of view. For a one-point interior, 1VP with the point on the horizon inside the picture.
Snapping
With a ruler layer present, brush strokes on the drawing layer follow the ruler: a stroke started near one family of lines is pulled along it toward that vanishing point, so long edges of buildings and furniture come out straight and converging without a straightedge. The ruler has a snap mode that can be set to none when you want the lines as a visual guide only, which is the right setting for loose sketching over the construction. Toggle the ruler layer's visibility to hide the lines while keeping the file's rulers for later.
What SAI cannot do
There is no fisheye or curvilinear ruler, no camera model (the ruler does not know what lens the vanishing-point spacing corresponds to), and no scale: the ruler gives directions, not sizes. Those three gaps are what the grid tools here fill.
A lens-accurate grid from this site
Open the 2-point perspective grid, set the lens and rotation for the shot (35 mm and 30° is a natural street corner; 24 mm for a wide interior), set the camera height, and switch on the vanishing-point markers. Export a transparent PNG at your canvas size and open it in SAI as a layer at 30–40% opacity. Then create a Perspective Ruler and drag its vanishing points onto the marks in the exported grid: SAI's snapping now matches a real lens, and the grid's one-metre squares give you sizes the ruler lacks. For curvilinear work, export from the fisheye grid and draw over it without a ruler.
Common problems
Strokes snap to the wrong point. The stroke's first direction decides the family; start each stroke clearly along the edge you mean, or set the snap mode to none and draw freehand over the visible lines.
Vanishing points too close together. The view looks like a 16 mm lens. Move them apart; on the grid here that is a longer lens. A 35 mm view puts the points roughly 1.5 canvas-widths apart for a 30° rotation.
Ruler disappears. It is a layer: check it is not hidden, and that the active layer is the one you expect when painting.
Related
2-point perspective grid · Clip Studio perspective ruler · Krita perspective assistant · perspective basics · perspective drawing tools compared
Questions
Does PaintTool SAI have a perspective ruler?
SAI Ver.2 does: a Perspective Ruler with one, two or three vanishing points, plus Vanishing Point, Parallel Line, Concentric Ellipse and Symmetric rulers, all created from the layer panel as ruler layers. SAI Ver.1 has no perspective tools at all; if you are on Ver.1, the workaround is a grid image on its own layer.
How do I snap my strokes to the perspective ruler in SAI?
Select the ruler layer (or keep it active) and paint on your drawing layer; strokes follow the ruler's lines toward the nearest vanishing point. The ruler has a snap mode that can be set to none when you want the lines visible but not snapping.
How do I move or rotate a vanishing point in SAI?
Drag the vanishing point's control point. Alt + drag on a control point rotates the ruler; Shift + Ctrl + drag moves it. Vanishing points can be placed outside the canvas, which is where they usually belong for a natural lens.
Can SAI do fisheye or curvilinear perspective?
No. SAI's rulers are linear only: one, two and three vanishing points, parallel lines and ellipses. For a fisheye or 360° grid, export one from the curvilinear grid tool here as a PNG and use it as a reference layer.
Where do I find the rulers in SAI Ver.2?
In the layer panel: the New Layer menu includes ruler layer types, and the perspective ruler's own menu on the layer panel offers the related rulers. Rulers are layers, so they can be hidden, reordered and kept with the file.
How do I get a lens-accurate grid into SAI?
Build the view on the 2-point grid here, note where its vanishing points and horizon land, export a transparent PNG, and open it in SAI as a layer at reduced opacity. Then create a Perspective Ruler and drop its vanishing points onto the exported grid's marks, so the snapping ruler matches the lens.
A new lesson and a new grid, about once a month.
Each lesson arrives by email before it goes on the site, with the grid it was drawn on and the link to open it. Subscribers also get both free starter packs and the subscriber price on the paid ones. Never more than two emails a month; one click to leave.
Handled by Kit on our behalf. Your address is used for this letter and nothing else — see the privacy page.