Most Christians believe in the Trinity.

There are approximately 2.1 billion Christians in the world, counting all denominations. Of nontrinitarian denominations, these are the largest, listed with their number of adherents:

Christadelphians: 50,000

Christian Scientists: 400,000

The Church of Jesus Christ of Latter-day Saints: 15.5 million

Dawn Bible Students: 60,000

Friends General Conference: 35,000

Iglesia ni Cristo: 3-10 million

Jehovah's Witnesses; 8.5 million

Living Church of God: 50,000 (best estimate)

Members Church of God International: 13.7 million (wildly optimistic estimate)

Oneness Pentecostals: 24 million

Seventh Day Church of God: 300,000 (wildly optimistic estimate)

Unitarian Universalist Christians: 200,000 (wildly optimistic estimate)

United Church of God: 145,000 (wildly optimistic estimate)

Shepherd's Chapel: 10 million (wildly optimistic estimate)

Combined, total membership of all of these denominations is under 90 million. If I generously round up to 100 million, then 4.76% of all Christians are nontrinitarians.