To sketch an object in isometric, read its width, depth and height from the orthographic views, then draw each along its own axis. Build the base first and add the upper parts on top of it.
This lesson belongs to pictorial representations. If the three views still feel separate, revisit relating front, top and side views first.
What are the isometric axes?
There are three: one vertical, and two that rise at 30° to the horizontal. In this lesson, width runs up to the right, depth runs up to the left and height runs straight up.
Lengths along these axes are drawn at their real size. A 50 mm width becomes a 50 mm line at 30°.
Worked example: a stepped block
The front view is an L-shape. The left part is 20 mm wide and 40 mm high. The right part is 30 mm wide and 15 mm high, so the total width is 50 mm.
The top view is a rectangle 50 mm wide and 30 mm deep, with one vertical line 20 mm from the left. Both parts run the full depth.
- Mark the lowest front corner A. Draw the base edge 50 mm along the width axis.
- From A, draw 30 mm along the depth axis. Complete the base parallelogram.
- Raise 15 mm from every base corner, to give a slab 50 × 30 × 15.
- On the left 20 mm of the slab, raise a further 25 mm, so that part reaches 40 mm. Top face: 20 wide and 30 deep.
- Darken the visible edges and leave out everything hidden.
As a check on your corners, the front top of the tall part is 40 mm above A, and the front edge of the step’s top is 15 mm above the base. The difference, 25 mm, is the height of the vertical face you can see between them.
The mistake: measuring along slanted edges
A common slip is to draw the top of the step as a slanted line measured 20 mm long. That line is not on an axis, so its length on the paper is not its real size.
| Step | Wrong | Right |
|---|---|---|
| Locating the tall part | Measure 20 mm along a slanted edge | Mark 20 mm along the width axis |
| Height | Drawn at 30° | Drawn vertical |
| Result | Tall part too short or leaning | Tall part sits square on the slab |
The fix is to ask one question before drawing each line: which axis does this edge follow? If the answer is none, find its end points first and join them.
A quick self-audit
Before you finish, check three things. Do all vertical edges stand straight up? Do edges that were parallel in the views stay parallel in the sketch? Does the sketch show the same width, depth and height as the views?
Check yourself
The front view is a rectangle 40 mm wide and 30 mm high. The top view is a rectangle 40 mm wide and 25 mm deep. A rectangular notch, 10 mm wide and 10 mm deep, is cut through the full depth from the top, centred along the width. Describe the isometric build.
Answer
Start with a block 40 × 25 × 30 mm. The notch is centred, so 15 mm remains on each side: (40 − 10) ÷ 2 = 15.
Mark 15 mm from the left along the width axis on the top face, then 10 mm more. Draw the notch edges 10 mm down from the top, running the full depth of 25 mm along the depth axis. The notch floor sits at height 30 − 10 = 20 mm.
What to study next
Compare your sketches against the comparison checklist for pictorial-view mistakes, and see how oblique drawing treats lengths differently.
If you want a teacher to set fresh objects and review your sketching sequence, see online one-to-one Engineering Drawing tuition.