NEW YORK » Mayor Bill de Blasio is so tall that city workers had to build an oversize podium for him, installing a custom sliding step that can be pulled out for shorter speakers.

His albatross-scale arm-span is so wide that aides have trained him to avoid expansive hand gestures, to keep from accidentally smacking people nearby.

His legs are so long that the mayor insists on traveling in the front passenger seat of his city-issued SUV, avoiding a cramped back seat but possibly exposing himself to greater security risks.

In a city defined by its verticality, de Blasio’s Bunyanesque build has proved to be a political bonanza, allowing him to tower over smaller rivals and command a crowded room just by entering it.

But the tallest mayor in New York’s modern history is discovering that bigness can also be a burden, requiring a host of ergonomic adjustments and feats of stagecraft in City Hall.

There is the mayoral necktie, whose knot-to-length ratio has come under scrutiny. Average-size aides struggle to keep up with his long stride. At briefings, de Blasio adopts a studied hunch, to reduce the distance between his chin and the top of a commissioner’s head.

The mayor’s size has quickly become a source of fascination – and speculation.

De Blasio has long described himself as 6-foot-5. But doubts about that measurement have lingered among skeptical tall people who have stood shoulder-to-shoulder with him and wondered if the mayor understates his height.

Those doubts, it turns out, were well-founded.

After an inquiry this week, aides to de Blasio acknowledged that the mayor is nearly an inch taller than he has publicly let on.

De Blasio stands 6-foot-5-and-7/8, according to a study commissioned by his office.

"The man I’ve known for 22 years is not what he appears to be," said Chirlane McCray, de Blasio’s wife, who is 5-foot-3-and-1/2 and, according to aides, wielded a household tape measure to conduct the test. (The mayor was not made available for an independent review.)

The mayor is said by friends and colleagues to be proud of his stature and keenly aware of its impact, particularly in the highly symbolic realm of politics.

But de Blasio, who declined to be interviewed for this article, can also be sensitive about his height, concerned about appearing silly or out of place.

"He knows what it feels like to be the strange one in the room," said Bertha Lewis, a 5-foot-6 friend of many years.

Eager to put shorter companions at ease, the mayor has developed physical techniques: a reassuring hand on the shoulder, a half-hug greeting that is warm, but not enveloping. Call it a gentle-giant vibe.

"There’s a fine line between being tall and engaging, and being intimidating and looming," said Robert E. Cornegy Jr., a 6-foot-10 former basketball star and city councilman, who has discussed matters of tallness with de Blasio.

"You can be warm and inviting, and with one gesture, that can change sharply," Cornegy said. "I imagine the mayor goes through that same internal dialogue every time he has to encounter somebody."

Still, de Blasio’s height can often prove awkward. Even his embrace requires some delicacy on the part of the recipient.

"I love the mayor, and I want to be hugged by the mayor," said Jimmy van Bramer, a 5-foot-7 city councilman from Queens. "But he’s so tall that sometimes I’m not sure where to go in for the hug."

Staff members who have walked beside de Blasio recalled having to jog to maintain conversation.

"It’s always a little bit of a race to keep up with Bill," said Peter Colavito, a former chief of staff, and a mere 5-foot-10.

Height, or lack thereof, has an outsize place in City Hall history. Three-time mayor Fiorello H. La Guardia, the 5-foot-2 "Little Flower," drew comparisons to Napoleon; critics of John V. Lindsay, 6-foot-4, once asked if he was "too tall to be mayor."

Aides to de Blasio are quick to point out his advantages. Eye contact is rarely a problem. There is no risk of being lost in a crowd. (De Blasio’s shorter predecessor, Michael R. Bloomberg, 5-foot-7, who exaggerated his height on his driver’s license, had a tendency to vanish in groups.)

But the mayor is also deeply protective of his public image, and he often takes great pains to avoid appearing abnormally large.

Last fall, de Blasio insisted on bringing his own podium to a much-anticipated event at a hotel in lower Manhattan, where he was to share the stage with Bloomberg.

But organizers balked at the boxy, cumbersome lectern his aides shipped in for the occasion, which clashed with the hotel’s sleek dicor.

De Blasio’s aides were adamant: The hotel’s shorter lectern was not acceptable.

Finally, perplexed audience members watched as workers removed an elegant Plexiglas lectern and replaced it with a clunky black music stand, a compromise, from which de Blasio delivered his talk.

This particular issue will not be a problem at City Hall. Before de Blasio took office Jan. 1, city workers were instructed to create a taller version of the official mayoral lectern.

A longer microphone stick was added, along with a sliding footstool, complete with rubberized grip, to accommodate shorter people. (The mayor’s team had previously been forced to improvise: an aide was tasked with lugging a portable step stool to events.)

Sometimes, the mayor’s height can make him conspicuous in more complicated ways.

Security experts say de Blasio’s penchant for riding in the front seat of his city-issued SUV – a break from his predecessors, who sat in the back – is troublesome. Front windshields cannot be tinted, they point out, and the guards who ride with the mayor lose an unobstructed view of the road.

"It is highly unusual for the protectee to sit in the right front seat and have the bodyguard sit behind him," said Robert Tucker, chief executive at T & M Protection Resources in New York. Sitting in the back seat, Tucker said, provides for safety advantages "that are being compromised by allowing him to sit there."

If de Blasio’s size can be problematic at times, the power of his appearance has not been lost on those who share the political spotlight.

Michael Mulgrew, the 6-foot president of the United Federation of Teachers, said he used to loom over the shorter Bloomberg at public events.

Nowadays, he said, it is the mayor who stares down at him.

"My members were like, ‘You look small all of a sudden,’" said Mulgrew, recalling a recent joint appearance.

"I was like, ‘Yeah,’" Mulgrew added. "’I guess I do.’"