How many Lego bricks can be stacked one on top of the other before one at the bottom destroys?

It’s not what you think!

It’s a question that’s piqued the interest of the internet’s brightest minds, but there’s been no conclusive solution until now.

How tall can a Lego tower be built before the bottom bricks buckle under the weight?

Engineers from the Open University have finally solved the puzzle, and here’s a hint: it’ll be bigger than you think.

The answer was discovered thanks to the BBC‘s More or Less series, which encouraged academics to get into their labs and test it out on a hydraulic press.

Dr. Ian Johnston, an engineering lecturer and applied mathematician, told the broadcaster: ‘It’s an exciting thing to do because it’s an entirely new question and new questions are always interesting.’

Lego is famed for its tenacity, with the business engaging 4,000 South Korean children to build a record-breaking tower in Seoul this Spring that stands at a startling 105 feet tall.

Tallest Lego tower in Seoul, South Korea. Credits: Arch20

However, every building material has a theoretical limit beyond which it cannot be utilised, and it would be prudent to determine how much damage the plastic bricks can take before creating any taller Lego towers.

Researchers need to know two things to figure out how tall a structure can be before it collapses: the total mass of the building material employed and its yield strength.

This is the amount of pressure a material can withstand before breaking. Dr. Johnston’s team tested it by placing a vulnerable-looking 2×2 Lego brick on a metal plate above a hydraulic ram.

A second plate coupled to a load cell was placed across the brick to measure the force pushing upwards. They then put on their safety glasses and backed away gently.

They soared through 3,500 Newtons of force on the hydraulic testing machine, which is the equivalent of 350kg (a third of a tonne) of force pushing down on the brick.

After achieving what Dr Johnston described as its’material collapse,’ the load eventually reached a staggering 4,240 Newtons – equivalent to 432kg – and the brick slowly began to deform.

Repeating the experiment revealed that a standard 2×2 Lego brick constructed of ABS plastic can support a mass of 432kg. It was simple to find out how tall a Lego tower could be once that figure was known.

With an average 2×2 Lego brick weighing 1.152g and a total mass of 432kg, dividing the former by the latter yields the total number of bricks that a single Lego brick can support: 375,000.

When you double it by the height of the brick, 9.6mm, you can hypothetically build a 3.5km (2.17 mile) Lego tower before the one at the bottom has any problems.