How much grout do I need per sq ft?

Sq/ft of what? Tell us the size of your tiles or whatever you are using.

Tec has a calculator on their site:

http://www.tecspecialty.com/content/...alculator.aspx

but it all comes down to tile size, grout joint,tile thickness, tile pattern if multiple sizes are used, so there's no generic answer to your question. For 1/8", you can use either sanded or unsanded, under 1/8, then unsanded, over 1/8, then sanded, doesn't matter floor, wall or ceiling.

For multiple tile size patterns, figure out the total square footage of each pattern repeat, then figure out the percentage of the pattern is created by each size of tile. Combine all the tiles of the same size in the percentage calculation, for example, if the pattern was 1 12x12, 1 6x12 and 2 6x6's, the total sf of the pattern would be 2 sf, the 12x12 would cover 50%,the 6x12 25 % and the 6x6 25 % so in a room of 300 sf, 150 sf would be 12x12, 75 sf would be 6x12 and 75sf would be 6x6. On the calculator above, you would input each tile size and it's square footage one tile at a time. Each time you do the calculation of a tile size, write down the calculated poundage of grout and add them all together to get to your grand total of grout needs.