Chris Nyambura was raised Catholic but over the past six months he has started calling himself Buddhist. Aged 23, he is a graduate student in chemical engineering. Like many of his generation, especially on the American West Coast, he appreciates the emphasis on mental development and self-help in the spiritual practice he has chosen.

He belongs to a group of people who turn up every Sunday evening for guided meditation sessions in a small, brightly lit studio in downtown Seattle. This is one of 38 centres across the United States (and 679 around the world) affiliated to the Diamond Way movement, which has popularised a modern form of Tibetan Buddhist practice, that emphasises the practical over the arcane. Their teacher coaches them in techniques like visualisation and chanting as well as explaining some basics of the religion to any newcomers.

Mr Nyambura eagerly lists the ways in which, he feels, this practice benefits him. First, training the mental faculties. “A lot of people take refuge in relationships, food, material things. Part of Buddhism is trying to teach me how do I take refuge in my own mind.” Second, a sharper sense of cause, effect and accountability. “One of the things when we meditate is remembering how former thoughts, actions bring you to your present state and what you do now will ultimately shape your future.” Third, learning to live in the moment. “When you meditate, one of the first things is that you calm your mind and just rest in the present…”

Buddhism in the United States may be a large and prolix phenomenon, ranging from ethnically defined groups which foster community and ritual to the more individualistic approach epitomised by those Seattle classes. But almost everybody who studies the subject agrees that the religion is growing. Pew, an independent research body based in Washington, DC, reckons that by 2020 the number of American Buddhists may have risen to at least 4.2 million from 3.6 million in 2010. It is also growing in public esteem; last year, when Pew surveyed the feelings of Americans towards various religious groups, the youngest cohort of respondents (aged 18-29) gave top marks to Buddhism.

Today you can find in the United States outposts of virtually every form of Buddhism practised in Asia, says Scott A. Mitchell of the Institute of Buddhist Studies in California. The faith’s first significant presence on American soil came with Chinese immigrants in the mid-19th century; newcomers from Japan arrived a few decades later. Over time, non-Asians were drawn in. After 1945, a Japanese movement known as Soka Gakkai International, favouring chants rather than meditation, gained followers in the United States, including African-Americans and Latinos. (This cuts across a stereotype which holds that most converts to Buddhism are liberal whites.)

Charles Prebish, professor emeritus at Penn State University and a Buddhist scholar, reckons that Pew’s estimates are on the low side. He also thinks that converts are gaining numerical preponderance as some Asian-Americans drift away from their family traditions and beliefs. In any case, there are some people who transcend the sociologists’ distinction between convert and “cradle” Buddhist: for example, young Americans who have grown up in deeply committed convert families. There are some prominent teachers of Buddhism who fit that description.

At its liberal edge, the boundaries of the religion, as practised in America, can be very fuzzy. For example, most Buddhists would agree that their faith’s core axioms include five moral precepts: don’t harm living things, don’t take what is not given, don’t engage in sexual misconduct, lie or consume intoxicants. But not all the Americans who call themselves Buddhist really know about these precepts, let alone practise them.

Then there is the fact that American culture, including corporate culture, has cherry-picked aspects of Buddhist life, such as the practice of mindfulness. Big corporations may employ full-time coaches on meditation which draw on Buddhist techniques. But that does not make the users of these practices into followers of Buddhism.

Still, Mr Prebish insists that the most accurate way to determine whether people adhere to that religion is simply to ask them. In his view, an adherent is someone who says, “I am a Buddhist,” and is clearly talking about the most significant part of his or her religious life.

In Mr Mitchell’s view, issues of politics and social justice are becoming a focal point for the large and disconnected Buddhist scene, prompting followers to cohere and connect more often. “There is definitely a sense of, what I should do as a Buddhist about this or that issue,” he says. There have been Buddhist initiatives in favour of the environment and against racism. Last year, a dozen or so prominent American Buddhist leaders signed a statement protesting over the effect on the vulnerable of the current administration’s policies; scores of others added their names. The authors explained that although Buddhism can take many different forms, “our commitment is to ease the suffering of all living things…” Whatever the merits of learning to meditate in a Seattle studio, that is not where the religion will stop.