A recipe for the perfect sandcastle has been defined by laboratory researchers in Amsterdam and Paris.
After hours of building beach sand columns to devise a mathematical formula, their mix is a delicate balance of 99% sand and 1% water.
Not too much water, they concluded - just enough to form small "bridges" between grains of sand, making them stick together.
"If this optimum concentration is used, sandcastles reaching five metres in height can be built," said a statement on a report in the the journal, Nature Scientific Reports.
The formula also sets out the desired height-to-base-diameter ratio and sand compacting force.
The findings are of interest for civil engineering and soil mechanics, fields which deal with structural stability, wrote the scientists.
"In addition, it explains the maximum height of, and provides us with a recipe to construct the perfect sandcastle."