The product of 16 and 42 is 672
You have to measure out the rectangle in your yard. 16 feet wide x 42 feet long.
A pool measuring 16x42 feet has a surface area of 672 square feet. This is equivalent to about 62.3 square meters. The dimensions suggest a rectangular shape, which can accommodate various recreational activities or swimming laps, depending on the depth of the pool. Overall, it's a sizable pool suitable for both relaxation and exercise.
You can buy a testing kit and test your water to see if there are any abnormal bacteria in your water that would be keeping the chlorine levels low. Otherwise, just add chlorine daily to keep your pool safe for swimming.
Depends how deep it is! 16 x 42 = 672 square feet 7.48 (us)gallons to 1 cubic feet 672 x 7.48 = 5026.5 gallons for every 1 foot of depth (eg 4ft deep = 20106 gallons)