CONTINUOUSWAVE

GIven that 1-cm3 of water weighs 1-gram:

How much does 1-foot3 of water weigh?

ANSWER = 62.43-lbs

Derivation:

(1-gram/1-cm3) × (2.54-cm/1-inch)3 × (12-inch/1-foot)3 × (1-kg/103gram) × (2.2046-lbs/1-kg) = 62.427-lbs/feet3

Fresh water or salt water, Jimh? Actually it's fresh. Saltwater averages 64.1 lbs/cubic foot. That is why many Boston Whalers sit higher in salt water than fresh. Imagine the waterline of a Boston Whaler sitting in the Dead Sea which averages 77.4 lbs/ cubic foot.

Aside: These facts are some of the important information that is eventually drilled into scuba divers heads after they spend countless $$ on furthering their diving education.

A couple of conversions that I somehow remember, but come in handy:

1 ft3 = 7.48 gallons
120,000 gallons of water = 1,000,000 lbs of water
128 ounces in a gallon
454 grams in one pound

I taught my kids how to do unit conversions using the train track or monorail method, and it's really handy to know this, as you really don't need formulas anymore.

https://www.katmarsoftware.com/articles/railroad-track-unit-conversion.htm

You have to like the metric system:

If 1-cubic-cm of water weighs 1-gram, then 1-cubic-meter weighs 1,000,000-grams or 1,000-kg.

1-gram/1-cm3 × (102-cm/1-meter)3 × (1-kg/103-gram) = 103-kg/1-meter3

How I learned how many pounds in a kilogram:

My doctor had an old fashioned beam balance scale to measure a patient's weight, the type where you stand on the scale and slide weights across a calibrated beam to find the balance point. The calibrated scale had a pivot at each end, so it could be inverted. One side of the beam read in pounds, the side other read in kilograms. I think the doctor liked to record the patient weight in kilograms in his charts.

On one visit, it so happened that when I stepped on the scale, I weighed 220-lbs. The nurse flipped over the calibrated beam to reveal the weight in kilograms--100 exactly. I felt a little lighter at 100-kg than I did at 220-lbs. Before that visit, I would have needed to look up the conversion. But ever since then, I've known the conversion factor in my head.

Assignment as the Operations Officer to the Public Works Department in a NATO Headquarters in Europe required a fast brain change. First to convert metric to US for a week or so then to think in metric. It's a great system.