For lengths, GCS can display feet & inches (5'3"), feet, yards, miles, centimeters, meters, and kilometers.
For weights, pounds, onces, tons, kilograms and grams. There's also two variant suffixes that can be selected for both pounds ("lb", "#") and tones ("tn", "t").
| Imperial | Game Metric | Real Metric |
| 1 inch (in.) | 2.5 cm | 2.54 cm |
| 1 foot (ft.) | 30 cm | 30.48 cm |
| 1 yard (yd.) | 1 meter | 0.914 meters |
| 1 mile (mi.) | 1.5 km | 1.609 km |
| 1 pound (lb.) | 0.5 kg | 0.454 kg |
| 1 ton | 1 metric ton | 0.907 metric tons |
| 1 gallon (gal.) | 4 liters | 3.785 liters |
| 1 quart (qt.) | 1 liter | 0.946 liters |
| 1 ounce (oz.) | 30 grams | 28.349 grams |
| 1 cubic inch (ci) | 16 cubic cm | 1 6.387 cu. cm |
| 1 cubic yard (cy) | 0.75 cubic m | 0.765 cubic m |
Temperature: When dealing with changes in temperature, one Fahrenheit degree is 5/9 the size of a degree Celsius. So a change of 45°F is equal to a change of 25°C. To convert actual thermometer readings, subtract 32 from the Fahrenheit temperature and multiply the result by 5/9.
Weight conversion is as you noted: 1 lb = 0.5 kg. Length as well: 1 yd = 1 m.
For consistency, all metric lengths are converted to meters, then to yards, rather than the variations at different lengths that the GURPS rules suggest.
Same for weights: all metric weights are converted to kilograms, then to pounds. (these are for when you enter them into a field...)
https://github.com/richardwilkes/gcs/tree/master/model/fxp this directory has the various length & width code (fxp stands for fixed-point, since GCS tracks most everything using fixed-point values so that we get consistent output).