How much portland cement to sand mixture for a strong concrete mix?

For a strong concrete mix, a common ratio is 1 part Portland cement to 2 parts sand and 3 parts gravel, often referred to as a 1:2:3 mix. This translates to 1 bag (94 lbs) of Portland cement to about 2 cubic feet of sand and 3 cubic feet of gravel. Adjustments can be made based on specific project requirements, but maintaining this proportion helps achieve optimal strength and durability. Always consider the water-cement ratio as well, typically around 0.4 to 0.6 for strength.