The United States has yet to change to the metric system due, in part, to the challenge in converting to another system because the grids of materials will not simply and rationally convert. There are two methods for converting: soft conversions and hard conversions.
Soft Conversions
Soft conversions from imperial to metric represent an exact conversion where the material dimension has not changed. For instance, 12 inches would have a soft conversion of 304.8 millimeters. Occasionally, the soft conversion will be rounded so that 12 inches has a soft conversion of 305 millimeters.
Hard Conversions
Hard conversions from imperial to metric are used in the building industry to make the metric units more rational. For instance, 12 inches would have a hard conversion of 300 millimeters. In this case, the actual dimension of the material changes so that building materials can easily conform to metric grids.
Imperial to Metric Soft Conversions
| LENGTH | AREA | VOLUME |
|---|---|---|
| 1 inch = 25.4 mm | 1 sq. in. = 645.16 mm2 | 1 cu inch = 16.387 cm3 |
| 1 foot = 304.8 mm | 1 sq ft = 0.093 m2 | 1 cu foot = 28,316.847 cm3 |
| 1 yard = 914.4 mm | 1 sq yard = 0.836 m2 | 1 cu yard = 0.7646 m2 |
| 1 mile = 1.609 km | 1 acre = 4,046.86 m2 | 1 gallon = 3.785 L |
| 1 sq mile = 2.59 km2 |
Metric to Imperial Soft Conversions
| LENGTH | AREA | VOLUME |
|---|---|---|
| 1 mm = 0.0394 in | 1 mm2 = 0.00155 sq in | 1 m3 = 35.3147 cu ft |
| 1 m = 3.281 ft | 1 m2 = 10.7639 sq ft | 1 L = 0.264172 gallons |
| 1 km = 0.621 mi. | 1 hectare = 2.47105 acres | |
| 1 km2 = 0.368 sq miles |
