Draw a Glass of Water: Rim Ellipse, Refraction Line, and Cast Shadow

Object Drawing Lessons

This lesson teaches a reliable method for drawing a simple glass of water. You will build the glass from three checkable parts: the rim ellipse, the refraction line where the water surface meets the glass, and the cast shadow on the table. The method uses a defined convention for the rim ellipse and accepts valid stylistic alternatives. All measurements are hypothetical examples; measure your own paper and reference objects. The practice tasks are self-contained and can be solved from the text alone.

Practice materials: Printable downloads are not available for this lesson yet. Use the instructions and four exercises below.

Reference illustration

Use the stated measurements and conventions for each exercise.

Set the rim ellipse with a defined convention

Place the glass on a table at eye level or slightly above. The rim appears as an ellipse. Use this convention: the ellipse's horizontal axis is the full visible width of the rim; the vertical axis is the apparent height of the rim opening. Mark the horizontal axis first, then the vertical axis, then connect the four points with a smooth curve. This convention is a guide, not a universal answer; a flatter or rounder ellipse is valid if it matches what you see.

Check the ellipse by folding a scrap paper along the horizontal axis and holding it to the drawing. The top and bottom halves should mirror. If they do not, adjust the vertical axis. Keep the ellipse centered over the glass body.

1. Mark the left and right edges of the rim; connect them with a light horizontal line.
2. Mark the top and bottom of the rim opening on the vertical center line.
3. Draw a smooth ellipse through the four marks.
4. Fold-check the ellipse for symmetry and adjust.

Place the refraction line at the water surface

The water surface meets the glass at a second ellipse, lower than the rim. Draw a light horizontal line across the glass at the water level, then curve it slightly to follow the glass. This is the refraction line. Objects behind the glass appear shifted below this line; you can suggest this with one short offset line inside the glass.

Keep the refraction line parallel to the rim ellipse's horizontal axis. If the glass is tilted, the line tilts with it. Do not draw the water surface as a straight line across a curved glass; the slight curve is what makes the drawing read as a glass.

1. Mark the water level on the glass sides.
2. Draw a light curved line between the marks, matching the rim curve.
3. Add one short offset line inside the glass to suggest refraction.
4. Erase construction marks after the line is clear.

Add the cast shadow on the table

The cast shadow falls on the table opposite the light source. Decide the light direction first, then place the shadow on the opposite side. The shadow starts at the base of the glass and stretches outward. Its shape is a soft elongated oval or wedge. Keep the shadow darker near the base and lighter at the far edge.

Use a hypothetical example: if the light comes from the upper left, the shadow falls to the lower right. Measure the shadow length against the glass height; a shadow about half the glass height is a reasonable starting point. Label any numbers you choose as hypothetical.

1. Mark the light direction with a small arrow outside the drawing.
2. Draw the shadow outline from the glass base outward, opposite the light.
3. Shade darkest at the base and fade toward the far edge.
4. Check that the shadow does not cross the glass body.

Refine edges and check the whole drawing

Refine the glass outline so the sides taper slightly toward the base. The rim ellipse should sit centered on the body. The refraction line should be lower than the rim and parallel to it. The cast shadow should touch the base and fall opposite the light.

Use a simple check: measure the rim width and the base width with a ruler. In a typical tumbler the base is slightly narrower; record your own ratio as a hypothetical example. Confirm the water line is between rim and base, and the shadow is on the correct side.

1. Darken the final glass outline and rim ellipse.
2. Confirm the refraction line is parallel to the rim.
3. Confirm the shadow direction matches the light arrow.
4. Erase all construction lines and sign the study.

Worked example

Draw a glass of water on a table. The glass is 10 cm tall, the rim is 6 cm wide, and the water level is 4 cm above the base. Light comes from the upper left. Use the rim ellipse convention, a refraction line, and a cast shadow.

Four practice exercises

Common mistakes

• Drawing the rim as a perfect circle. Use the horizontal and vertical axis convention to make an ellipse; check with the fold test.
• Drawing the water surface as a straight line across a curved glass. Curve the refraction line slightly to follow the glass, parallel to the rim ellipse.
• Placing the cast shadow on the same side as the light. Mark the light direction first, then place the shadow opposite it.
• Making the shadow cross the glass body. Start the shadow at the base and stretch it outward on the table only.

Self-check rubric

• Rim ellipse uses the horizontal and vertical axis convention and passes the fold check.
• Refraction line is lower than the rim and parallel to the rim ellipse.
• Cast shadow touches the base and falls opposite the marked light direction.
• Glass sides taper slightly toward the base and the rim is centered.
• Construction lines are erased and the drawing is clean.
• Valid stylistic alternatives are accepted if the three checkable parts are correct.

Questions and answers