How much sand and cement needed to lay and fill 200 hollow blocks

I'd get two tons of red building sand and about 12 cement that may well do it if your short it will only be a bit you don't want to order Too much if your stuck with Aton of sand it's a bind moving it , use a bell cement mixer put in three quarter bag of cement and fill with sand add water as you fill get the right consistency about half a cup of feb mix

You can find many building material calculators online, just google something like, 'building calculators' and see what they say. To deal with the hollows, do they need filling? You could just fill them with sand but if you want to concrete them go for a mix about 5:1. Same on the mortar for laying them. If you are using a separate liner then that's good, if not you will need a slurry to waterproof it. Ask your local builders merchants about this. To calculate the hollow size, measure the size of one of the hollows, length, width, height, and then multiply by the number of hollows, so it is likely to be something like 150mm x 150mm x 150mm x 400 (Assuming each block has two hollows and there are 200 blocks.) The above gives you: 1,350,000,000. Divide this by 1,000,000 to convert to litres: 1,350. So you would need 1.35t or two bulk bags of sand and cement total at whatever ratio you choose to go for. So at 5:1 you would buy 14 x 20kg bags of cement and two bulk bags of sand. You will have quite a bit of sand left over, roughly half a bag but you can use that in your mortar for building these walls. Hope that helps! Feel free to send me measurements of one of the holes and I'll do the maths for you.