How to dimension an isometric drawing

An isometric sketch shows the shape; dimensions turn it into something you can build. The rules are the ones you’d use on a flat drawing, plus one more: every dimension lies in the plane of the face it measures.

A 50 × 30 × 30 mm block, one dimension per axis.

The four parts of a dimension

Extension lines, dimension line, end marks, number.

Leave a small gap where extension lines leave the part, and run them a little past the dimension line. Note the units once for the whole sheet.

Rules for isometric dimensions

Six rules, one per tile.

Decide which face an edge belongs to; its extension lines follow that face’s other direction. A slope is foreshortened, so locate its two ends along the axes instead.

Aligned or unidirectional text

Aligned tilts with the line; unidirectional stays level.

Drafting practice accepts both, so pick one per drawing. Aligned is faster by hand, because you write along the line you just drew.

A worked example

Draw the block

Width: 50

Height: 30

Depth: 30, units once

Three dimensions, one per axis, and the block is fully defined. Then locate holes, slots and cutouts from edges you’ve already dimensioned.

Dimensioning in PencilCAD

Dimension: drag corner to corner.

PencilCAD is a pad of isometric paper with CAD-style dimensions built in.

Open More and choose Isometric paper: Small, Medium or Large.
Tap the toolset chip beside the page count and choose CAD, or use Settings → Tools.
Sketch with Line. Lines snap to the lattice and weld.
Pick Dimension on the rail and drag from corner to corner.
Tap the units chip at the top right for units, fractions and what one square stands for.
A pad holds up to 50 pages, saved as you draw.

More guides

2D CAD on iPad
What 2D CAD needs, how a Pencil workflow differs from a mouse, and when you still want a desktop.
Isometric paper on iPad
What the lattice is for, how to sketch a part on it, and which size to pick.
Drawing to scale on iPad
Pick a scale, count squares, work out slanted lines, and keep every line on the grid.
Sketching a floor plan to scale on iPad
Measure the room, draw walls at their real lengths, add doors and dimensions, and print at 1/4″ = 1′.
Parametric sketching with Apple Pencil
Dimensions and constraints, degrees of freedom, and how to fully define a sketch.
Tracing a photo to scale on iPad
Shoot it square, pick a reference length, set the scale, and check it before you trust it.
Make Cricut cut files on iPad (SVG, to scale)
Pick a mat preset, nest copies, set cut, score or draw, add single-line text, and hand the SVG to Cricut Design Space at true size.
Sketch to G-code for a CNC router on iPad
Profile, pocket and V-carve toolpaths with tabs and ramps, a preview to scrub through, one G-code file per tool, and upload over Wi-Fi.
Sheet metal flat patterns on iPad (bends, K-factor, DXF)
Bends with angle, radius and K-factor, flanges and bend checks, then a flat DXF with a BEND layer for the shop.
Laser cutting on iPad
Bed presets, cut, score and engrave per layer, preflight and a kerf test, a power and speed test grid, and files for laser software.
From iPad sketch to DXF
Draw at true size, keep outlines clean, pick units and layers, and open it in Fusion or a laser cutter.
Sketching woodworking plans on iPad
Overall sizes, a page per part, joints in detail, and a cut list before you cut.
Sketch it first: planning a 3D print on paper
Must-fit sizes, clearances, print orientation and wall thickness before you open CAD.