The conversion for riprap varies by size but generally speaking, a conversion of 2 tons per cubic yard is sufficient. Limestone has an in situ unit weight of approximately 160 pounds per cubic foot but voids on average reduce the unit weight of riprap to closer to 150 pounds per cubic foot.
If you mean uncrushed, it would be somewhere on the order of 2.6 tonnes (2600 kg), give or take a bit depending on what exactly is in it. Crushed limestone would have a lower density, generally about half the solid density, depending on grain size of the crushed product (which affects the amount of open space between the grains).
MOT Type 1 Sourced from our Gill Mill and Duns Tew quarries, MOT Type I Limestone is ideal for oversite, trench and sub-base in the construction of highways and carparks. Mot Type 1 is simply crushed Limestone that meets the requirement of the Department of Transport Specification for Highway Works, clause 803.
The densities (pounds per square foot, or tons per cubic yard, sometimes called "pounds per foot" or "tons per cube") will also vary according to the season, the saturation levels (dampness) of the piles of medium when you purchase the mediums, the quality of the sieves used to sort the crusher runs, and so forth.
1 kilogram/cubic meter is equal to 1.5747304441777E-7 stone/(cubic centimeter), or 0.001 tonne/cubic metre. Note that rounding errors may occur, so always check the results. Use this page to learn how to convert between stones/cubic centimeter and tonnes/cubic meter.
They average about 175 pounds per cubic foot. To estimate the quantity, you need to convert the area into cubic feet by multiplying length x width x height. Once you have this number, multiply it by the boulder's weight per cubic foot, then divide by 2000 to convert this number into tons.