Unit Conversion Mistakes That Cost Real Money
The five unit conversions that go wrong most often, the exact factors, and how a single factor-of-two error doubles a material order.
Factor of two
Radius versus diameter, and radius squared for area. Doubling the radius quadruples the area — the single most expensive geometry error on a site.
Metric versus imperial in construction
A 9-inch wall is 229 mm, not 225. Over 100 feet that is a 4-inch drift, enough to misalign a room.
Square versus cubic
Converting sqft to sqm uses 0.0929; converting cubic feet to cubic metres uses 0.0283. Using the wrong one under-orders concrete by a factor of three.
Weight versus mass in cooking
A cup of flour is about 120 g, a cup of sugar about 200 g. Volume conversions for dry ingredients are unreliable — weigh them.
Do the reverse check
After converting, convert back. If the number does not return, the factor was applied in the wrong direction.