Masonry Magazine December 1994 Page. 22
Metric Conversion
When converting from inch-pound units to metric units, it is important to use the correct conversion factors and to follow proper rounding procedures. Table 2 provides a list of common inch-pound to metric conversions.
An example of incorrect metric conversion would be converting 8'-8" to 2.4 m - 203 mm. The correct conversion of 8'-8" would be 2.64 m. In addition, fractions are never used in the metric system, decimals are used instead. For example, a length of nine and one-half meters is written as 9.5 m, not as 9-1/2 m.
Rounding
When converting inch-pound units to metric, use the same number of digits as there were in the inch-pound number. Twenty-five feet multiplied by 0.305 m/ft equals 7.625 m, which is then rounded to 7.6 m.
The use of metric units in construction should not affect established tolerances. Dimensions on building plans are rarely shown to less than 1/8 inch (3.2 mm) because it is impractical to build to a tighter tolerance. Hence, it is meaningless to state dimensions in decimals of millimeters. For example, a typical concrete masonry mortar joint is 3/8 inch thick. The exact metric conversion is 9.53 mm, so this is rounded to the nearest whole number, 10 mm.
Concrete Masonry Unit Dimensions
Because concrete masonry uses soft metric conversion, the metric equivalents of concrete masonry unit dimensions are simply the exact metric conversions of the inch-pound unit dimensions. This is illustrated in Figure 1 for an 8-inch (8 x 8 x 16) concrete masonry unit. Table 3 lists the inch-pound and metric equivalent dimensions for typical concrete masonry units of various sizes.
Table 2-Inch-Pound To Metric Conversions
| Quantity | to convert from these inch-pound units... | to these metric units... | multiply the inch-pound units by: |
|---|---|---|---|
| Length | mile (mi) | kilometer (km) | 1.609 |
| | foot (ft) | meter (m) | 0.305 |
| | foot (ft) | millimeter (mm) | 305 |
| | inch (in.) | millimeter (mm) | 25.4 |
| Area | square yard (yd³) | square meter (m²) | 0.836 |
| | square foot (ft³) | square meter (m²) | 0.0929 |
| | square inch (in.²) | square millimeter (mm²) | 645 |
| Volume | cubic yard (yd³) | cubic meter (m³) | 0.765 |
| | cubic foot (ft³) | cubic meter (m³) | 0.0283 |
| | cubic inch (in.³) | cubic millimeter (mm³) | 16,367 |
| Mass | pound (lb) | kilogram (kg) | 0.454 |
| | kip (k) | metric ton (t) | 0.454 |
| Mass Density | pounds/cubic foot (lb/ft³ or pcf) | kilogram/cubic meter (kg/m³) | 16.02 |
| Force | pound (lb) | newton (N) | 4.448 |
| | kip (k) | kilonewton (kN) | 4.448 |
| Force per Unit Length | pound/foot (lb/ft or plf) | newton/meter (N/m) | 14.59 |
| | kip/foot (k/ft) | kilonewton/meter (kN/m) | 14.59 |
| Force per Unit Area | pound/square inch (lb/in² or psi) | megapascal (MPa) | 0.00689 |
| | kip/square inch (k/in.² or ksi) | megapascal (MPa) | 6.89 |
| | pound/square foot (lb/ft² or psf) | pascal (Pa) | 47.88 |
| Bending Moment | foot-pound (ft-lb) | newton meter (N·m) | 1.356 |
| | foot-kip (ft-k) | kilonewton meter (kN·m) | 1.356 |
| Thermal Resistance (R-Value) | square foot-hour- degree Fahrenheit/British thermal unit (ft²-hr-°F/Btu) | square meter degree Celsius/ Watt (m²·°C/W) | 0.176 |
| Thermal Conductance (U-Factor) | British thermal unit/square foot- hour-degree Fahrenheit (Btu/ft²-hr-°F) | Watt/square meter degree Celsius (W/m²·°C) | 5.678 |
| Temperature | degrees Fahrenheit (°F) | degrees Celsius (°C) | °C = (°F - 32)/1.8 |
Example: The actual length of a typical concrete masonry unit is 15-5/8 in. To convert this length to metric, use the conversion factor from the table above, 25.4. The converted actual length = 15.625 x 25.4 = 397 mm.