Jonathan Miller is into size.

That means stepping into closets. It means sliding into hidden places. It means calculating length and width. It means dealing with exaggerations. It means doing all this year round in Manhattan, where size truly does matter.

“I’ve been doing this for 20 years,” Mr. Miller said. “And I tell you, I never get tired of it. When you’re having fun, it just oozes out of you.”

The fun includes figuring out the worth of what he measures. In his case, it’s mostly residential real estate. What he has to say is eagerly awaited every few months by Manhattan’s $10 billion residential real estate industry – buyers, sellers, the press, and a host of others who want to know how much their property has appreciated.

In real estate these days, virtually everything has appreciated – but perhaps none more than Manhattan’s residential space. So when Mr. Miller, co-founder and CEO of Miller Samuel Incorporated, produces his report, there’s not only a ready-made audience for it. The report triggers an instant buzz as New Yorkers calculate what their apartments are worth in the markets – or whether they can afford to enter that market at all.

What’s so special about Mr. Miller’s enterprise? Don’t the big realtors turn out inventories and list their prices anyway?

“Our reports are deeply analytical and sophisticated, yet they are produced in easy-to-understand language,” Mr. Miller said. “I’m brutal about being straightforward. People see your integrity. They see my record in the real estate business.”

The Boston-born Mr. Miller did not plan a career in real estate. His father, Donald, had done well in that industry, but he was also an eclectic entrepreneur who went on to other successes – such as owning McDonald’s franchises in the Caribbean and Latin America, establishing a cooking school in Washington, and founding the National Association of Cooking Schools.

“I was exposed to business from an early age because my father was a serial entrepreneur,” Mr. Miller said. “I was also exposed to his values – working hard but working smart, and being passionate about whatever it was that I wanted to do.”

What he set out to do after graduating from Michigan State University was to join an inner-city hospital as a department head in Chicago.

“But I didn’t find institutional work too exciting,” Mr. Miller said of his Chicago stint. “So I decided to get a real estate license.”

Wasn’t that a substantial leap from the hospital business?

“Yes – and everybody thought I was crazy,” he said. “Other than my family, I didn’t get a single word of encouragement.”

In the event, Mr. Miller found that the absence of such support didn’t matter. On his first day at a small real estate agency, he had no way of anticipating that within four months he would become the second-ranked broker there. It was an auspicious start. On that very first day, he found a buyer for a property. The other broker on the deal remains his friend and visits him periodically in New York.

New York was, oddly enough, a city Mr. Miller had never visited. One day, he and his wife, Cheryl, drove out to attend a relative’s wedding on Long Island. They passed through Manhattan.

“We were instantly sold on New York,” Mr. Miller said. “We moved from Chicago in four weeks.”

His parents, meanwhile, had also moved to New York from their home in Washington. Mr. Miller found a Japanese investor who offered $750,000 for him to start a brokerage. However, Mr. Miller decided against it. Then he approached his parents for a small loan, and used it to start an appraisal company, Miller Samuel.

He persuaded his parents to join him. He also roped in his wife and his sister Dina. They all had some sort of real estate experience – Mr. Miller had worked as a sales director at a realty company soon after arriving in New York. He was convinced that his new company was capable of building a reputation that would be truly unique.

He thought that the company’s very name, Miller Samuel (the Samuel on the shingle was the first name of a short-lived partner), would project not only uniqueness but suggest gravitas that the so-called old world businesses have.

What they did that no one else was doing was use computers and assemble what eventually became possibly the largest database about Manhattan’s coops and condominiums. Not only was the square footage listed, but also room count of apartment, location desirability, views, layout, and physical condition of the property.

Such information was collected through appraisals, which meant that Mr. Miller quickly became sought after by banks in the mortgage business and also by buyers who wanted a second opinion about their apartments.

Now the banks and financial institutions come to him from all over the country. His expertise is relied on by the federal government, including the Federal Reserve, the Internal Revenue Service, and New York City. Miller Samuel did more than $4 billion in evaluations in Manhattan in 2004.That number is expected to grow this year.

The aggregate data about Manhattan is issued in a thick report for which Mr. Miller has collaborated with Prudential Douglas Elliman since 1994. The single appraisals may not attract headlines, but his reports certainly do. The most recent said that the average Manhattan apartment now costs a staggering $1.3 million, a record.

What’s it like for a Boston Brahmin who grew up in Washington and went to school in the Midwest to function in New York?

“I’m always surprised how difficult some people here can be,” Mr. Miller said. “There’s always room for another nice person.”