Volume on Sight

Pick a few objects around you and estimate each volume in your head. A cereal box: length × width × height. A 28 × 18 × 6 cm box holds 3,024 cubic cm ≈ 3 liters. Check it against a 1-liter carton to recalibrate.

Now a soda can: a cylinder about 12 cm tall with a 3.3 cm radius. V = πr²h = π × 10.9 × 12 ≈ 410 cm³, close to the actual 355 ml once you allow for air space at the top. One afternoon of guessing like this and your volume intuition catches up with your length intuition.