How much does a LEGO brick weigh?
In most cases you can find the weight of a brick from Bricklink an unofficial LEGO site that takes weight measurements from user submitted data. Bricklink states the 1x4 brick as 1.64 grams in weight.

LEGO bricks tend to be odd weights because the design process primarily focusses on the physical aspect. A 1x8 and 2x4 brick both have exactly eight studs, yet the weight between them differs  by almost a gram. 

In the interest of scientific accuracy, I would recommend weighing the bricks yourself with digital kitchen scales to confirm the weight.