Based on my measurements, 25kg of grit is about 0.5 cubic feet.

I weighed some grit on a scale for you in a graduated cup:

• 0.5L grit = 0.835kg
• 25kg / .835kg = 30 * 0.5L
• 25kg = 15L
• 25kg = 0.5 ft^3

If you squish the bag a bit, it's around 10" diameter and 12" tall, which works out to 0.54 cubic feet.

Disclaimer: I used local granite grit, but it should be pretty much the same.

I need about 30 cubic feet of gritty mix.

Its recipe calls for equal volumes of bark fines, grit and Turface so I'll need about 10 cubic feet of each.

That is a lot of gritty mix. What are you planting in them? Just curious.

I just re-counted my pots and re-computed their volumes:

I'd appreciate it if someone would double-check my calculations.

Hi tropicofcancer:

To figure the gals and cu. ft. that my pots hold, I used:

http://www.harvesttotable.com/2015/11/container-and-pot-sizes-how-much-soil-do-i-need/

Assuming that the pot size to gallons is correct I think you are overestimating a bit when doing gallons to cubic feet conversion.

I gallon = 0.134 cubic feet

With the above conversion a 25 gallon will be 3.34 cubic feet. You have 3.80 in the last row. Second thing is the volume will be a tad bit less depending on how much to top of the pot you fill.

If you like you may try this site for getting a more accurate volume of pots. I like it since it uses the actual dimensions of the pot top/bottom and height. The answer is in cubic inches. To get cubic feet divide by 1728 (=12x12x12). See if you get different answers.

What is the link to the site for getting a more accurate volume of pots?

My bad. I forgot. Here it is: pot volume calculator

Select the inches, default is cm.

Using the pot volume calculator, I get 54 cu. ft.!

Assuming all the measurements and calculations are correct ( I mean the pot dimensions, then that should be the correct value. I am a bit surprised to see the higher value but then that must be it. Everything else looks OK to me.

The first time I computed the volumes, I came up with 32 cu. ft.

The next time, I came up with 47 cu. ft.

The latest time, I came up with 54 cu. ft.

(The number of containers and their sizes didn't change!)

For each time you calculated did you use a different method to find the volumes? I think the last method I provided is the most accurate since it takes into account the size and shape of the pot. You could check your numbers for some pots by plugging the holes (if feasible) and filling with water and then measure the volume of water it holds.

For my more-accurate measurements, go to:

http://forums2.gardenweb.com/discussions/3899050/cubic-feet-of-my-containers?n=3

and read my "Often, responses to original posts tend ..." response to tropicofcancer