Image copyright AFP Image caption The monument, honouring the first US president, was completed in 1884

The Washington Monument is actually about 10 inches (25.4cm) shorter than previously believed, surveyors say.

The stone obelisk was completed in 1884 and since then tour guides and others have dutifully quoted its height at 555ft and 5.13ins (169.3m).

But US government surveyors said on Monday the column is 554ft and 7.34ins.

Despite the shrinkage, it is still the world's tallest obelisk and by far Washington DC's tallest structure.

Made of marble, granite, and bluestone gneiss, the monument to the first US president is also the world's tallest stone structure. There are taller monumental columns elsewhere, but they are neither all stone nor true obelisks.

The monument has not become shorter, but rather measurements have become more precise.

Dru Smith, chief geodesist with the National Geodetic Survey, said that modern international standards for tall buildings call for a different base point than what was likely used in the 1880s.

Image copyright AP Image caption The surveyors used a different base point to determine the Washington Monument's new height

Image copyright AP Image caption The US Park Service plans to keep quoting the "historical height" rather than the new findings

Four brass markers were believed to have been used as the base for measurement in 1884. Today, those markers sit about 9ins below ground near each corner of the monument.

The markers could have been at ground level in the past, Mr Smith said. Recently, a new plaza was installed around the monument, and "it's clear that what was ground level has changed over the years".

The monument recently reopened in May 2014 after being closed for 32 months due to damage from an earthquake in 2011. The new survey was done as part of those repairs.

Despite the findings, the US Park Service - which operates the monument - is not about to part with the disputed 10 inches. Guidebooks and other purveyors of trivia are expected to remain unchanged.

"For our purposes we'll still use the historic height rather than the architectural height, since they're measured from different places," said Jenny Anzelmo-Sarles, a spokeswoman for the National Park Service.