Fact-Checking Coin Measurements: Is a Dime Exactly 17.91 Mm in Every Mint Year?

Find the essential facts concerning Fact-Checking Coin Measurements: Is a Dime Exactly 17.91 Mm in Every Mint Year.

Pull a 2026 Roosevelt dime directly from an uncirculated mint set, measure it across the widest point of the rim using a hardened carbide caliper, and you will likely read 17.90 mm to 17.92 mm. The legal specification of 17.91 mm represents a target median, not an absolute constant across every individual strike. The Mint operates under statutory tolerance bands defined in Title 31 of the United States Code.

Those minute variations stem from three physical dynamics:

First, the retaining collar determines diameter. When the coin is struck, the collar ring holds the planchet to prevent it from sprawling outward. As production runs churn through hundreds of thousands of blanks, the retaining collar undergoes friction fatigue. A collar near the end of its service life yields a fractionally wider coin than a brand-new collar installed at the start of the week.

Second, coin caliper measurement must account for the coin's orientation. Dimes are rarely perfectly circular down to the micrometer. Taking three separate measurements across different clock angles, measuring from 12 to 6, then 3 to 9, then 2 to 8, routinely produces spreads of 0.03 mm to 0.05 mm on the exact same piece of metal.

Third, rim height creates deceptive depth numbers. While reference manuals cite 1.35 mm as the standard dime thickness, that figure measures the elevated outer rim. The center of the coin, through the field beside Roosevelt's cheek, often measures barely 1.15 mm deep. Anyone modeling coin holders or custom hardware enclosures must account for this pronounced raised lip.