Using the previous post calculations
To calculate how much water to raise the oceans by 1 inch...simplified.
Volume of sphere: V = 4/3 x PI x Radius^3 (cube of radius)
Volume of the outer 1” ...V = 4/3 x PI x [(Radius + 1/12 foot)^3 - Radius^3 ]. (using 1/12 of foot instead of 1 inch...so that answer is in cubic feet vs. cubic inches.)
Given that radius of earth is about 4000 miles ...times 5280 ft per mile .
NOW - that is covering the entire surface of the earth 1 inch...but since the earth is 70% water and 30% earth - then take the computation - and multiply by 0.7 to get the volume to increase water level by 1 inch - but we are not putting water on the land mass to any appreciable amount.
Big numbers. Once you get volume - then convert volume to gallons? 1 cubic ft. of water is approximately 8 gallons.
That is it, using ‘back of envelope figure.