The tallest mountain in the UK has "grown" by a metre in height in the last 65 years, experts have discovered.
The change is not down to geological movement, but the improvements in technology that allow a more accurate reading than when the mountain was last surveyed in 1949.
The new height will be displayed on all new OS digital and paper maps.
The new measurement was made by positioning a survey grade GPS receiver at the summit of Ben Nevis for two hours. Data was constantly fed to satellites and then checked by OS experts before being confirmed.
In 1949, it took a team of seven surveyors 20 nights to obtain their calculation, OS said.
The new height is exactly 1,344.527m but is rounded up to 1,345m officially.
Mark Greaves, OS geodetic consultant, was the first person to discover the change.
He said: "The new height relates to the highest natural point on the summit and was measured as 1,344.527m.
"I double checked everything and asked others to do so too. What is amazing is how close the surveyors in 1949 were.
"The measured height has changed by centimetres, but those centimetres mean we now need to round up rather than down. So that's why Ben Nevis will now be officially known as 1,345m."
Field surveyor Angus Hemmings climbed Ben Nevis to check if repair work to the stone cairn at the peak had affected the trig pillar, a surveying station at the top of the mountain.
He said: "It was raining, sleeting and snowing at the summit, but harsh weather doesn't affect our equipment or readings. What it did do, though, was give me a greater sense of respect for the 1949 surveyors.
"Each day they hauled 200lbs of equipment up Ben Nevis and its surrounding mountains. They also had to wait till night, because strong lights were shone from the trig pillars of the other mountains on to Ben Nevis', which enabled them to collect their data.
"It took the surveyors 20 nights because they only had three clear nights in that period to get it right. To do the best possible job it had to be run with military precision, everything they did had to be timed to perfection. Their effort and accuracy is remarkable."
OS holds around 460 million geographic features in its database of the UK and regularly updates maps, with more than 10,000 changes possible each day.
OS marketing director Nick Giles said: "In reclassifying the height of Ben Nevis our map becomes even more precise.
"Now it's officially taller, I wonder how many will feel tempted to revisit its summit?"