View Full Version : estimating formulas

JJfishes

04-21-2006, 06:13 PM

Wondering if anyone knows of a site to get info on estimation of bulk materials needed, specifically base material for patios and walks. An example would be 100 square feet by 9 inches deep of COMPACTED material. How much base material do i need in tons or yards.

Thanks Jay

Bustus

04-21-2006, 06:52 PM

I'm not sure they are exactly what your looking for, but there have been posts on this topic. Just use the search function and I'm sure you'll find some formulas. Good Luck!

DVS Hardscaper

04-21-2006, 08:30 PM

I have a feeling you'll receive varied responses.

We have been doing full fledged hardscapin for 10 years. And have always been right on the money with the following formula:

TOTAL SF x inches / 3 / 27 = x 1.2 x 1.5 =

Ok I'll go further:

100 x 9 / 3 / 27 = 11.11 x 1.2 x 1.5 = 20 tons

dividing by 3 is what equates the inches

multiplying by 1.2 is what converts cu yds into tons

multiplying by 1.5 is what accounts for compaction.

This is the only formula I have ever used. (computerized estimating system does it for me), and I do know other folks have other good formulas.

http://www.outdoorfinishes.com

The way I do is take your SF x base thickness x 10 and divide by 2000

10 represents 10lbs per SF@ 1 inch compacted 2A modified stone

100 SF @ 9" = 100*9*10=/2000= 4.5 Tons

a 10X10 pad & 20 ton would equal a 40" base

cgland

04-22-2006, 09:39 PM

Andrew - Instead of dividing by 3 you should be dividing by 12. 20 tons for a 100 sq. ft. patio @ 9"! That's crazy! I came up with 5 tons or 4.99999 to be exact.

Chris

bigviclbi

04-22-2006, 09:55 PM

I'd be about 5 tons for 9" but I'd have to say it varies depending upon what you are using as your base.

Mike33

04-22-2006, 10:07 PM

This is really funny we get all different answers. I got 4.9 tons but with price of fuel of going back for a small quanity i would get 6 ton. I use sq.' divide by 27 multiply by 1.35 Was wonering how the 1 guy got 20 ton?

Mike

cgland

04-23-2006, 09:31 AM

This is really funny we get all different answers. I got 4.9 tons but with price of fuel of going back for a small quanity i would get 6 ton. I use sq.' divide by 27 multiply by 1.35 Was wonering how the 1 guy got 20 ton?

Mike

Mike - The price of fuel in no way affects the tonnage needed to cover that excavation!:dizzy:

Chris

Mike33

04-23-2006, 09:43 AM

Mike - The price of fuel in no way affects the tonnage needed to cover that excavation!:dizzy:

Chris

My point was formula was 5 ton. I would for this size job get a extra ton because of fuel prices i would not want to be a litttle short and where i have to go to get stone the fuel and time would hurt. You do have to look at your time and fuel these days you can always take a half ton away cheaper than holding the job up.

mike

mrusk

04-23-2006, 10:45 AM

I always over order base material. 90% of the time there is somewhere to dispose of it on site, since i don't have a dump truck.

Sometimes the customer gets real happy when i spend 5 minutes and fill in some pot holes on there driveway.

Pavers Plus

04-23-2006, 10:50 AM

for a 10'x10' area (100sf) at 9" deep, I'd figure on adding about 3" to the 9" to account for pre-compacted material. {if this 10x10 pad was in the middle of nowhere, don't forget that the dimensions would actually be closer to 11.5'x11.5' to account for the extra gravel needed on the perimeter to account for the depth and allow for the strength of the base- so really about 132sf}

Formula is as follows: [Area x Depth = Cubic Feet] [ divide Total cubic feet by 27 to get cubic yards] [multiply by factor to get tons (I use 1.65)] **also, I use decimals of feet instead of inches because it saves 1 step. IE: 6" equals .5', 9" equals .75***

100sf x 1' = 100 then divide by 27 to get from cubic feet to cubic yards = 3.7 cubic yards then multiply by either 1.35 or 1.5 to get your tonnage -- which would equal either 4.99 tons to 5.55 tons respectfully. I always estimate my gravel a little high anyway, so use a factor of 1.5-1.65 as a multiplier.

One more example which would be more commonly used on most of your installations....

100sf area with a 4" base would require approximately 3 tons. Lets see how we come up with that one.

100sf x .5' (6") = 50 cu.ft divided by 27 = 1.85 cu.yds multiplied by 1.65 equals 3.05 tons

the 6" accounts for about 2" in compaction to get to 4" depth.

As a rule of thumb, we usually tell homeowners or contractors that you need about 3 tons/100sf of gravel for a 4" compacted base (8" base would need about 5-6 tons). We also tell them about 1 ton/300sf of concrete sand for 1" setting bed. Hope this information helps some of you.

dccarling

04-23-2006, 11:41 PM

Number of square feet to be covered by base divided by 175 x number of inches of compacted base x 1.1 = number of US tons.

100 sq-ft 9" of compacted base requires 5.66 tons

southernlandscapespecial

04-23-2006, 11:46 PM

Try gardenplace.com

ma5tr

04-24-2006, 08:49 PM

Why do people make this way harder than it hased to be?

Decimal feet is the way to go...its the easiest.

if you must excavate say 9" you would divide 9" by 12"(because there is 12" in 1 foot) That will than give you your amount to be excavated in decimal form.

9"= 0.750 decimal feet.

Because you have 0.75 decimal feet of material to be added to 100square feet of area you multiply 100square feet x 0.75

=75(cubic feet)

Now there is 27 cubic feet in 1 yard of soil

You now take toyr 75 cubic feet and divide it by 27 (since there is 27 cubic feet in 1 yard of soil)

This gives you 2.77777777 yards

Now depending on material...your weight will vary, but I have found that for 3/4 crusher run or 'a' gravel the weight is about 1.5 times the amount of a yard material(dry 1.75 wet).

2.7777777 x 1.5 = 4.16666666666 tons or 4.86 tins wet (raining conditions)

Hope this helps

dccarling

04-24-2006, 10:46 PM

ma5tr,

You are right if you are just gona place the material in the excavated area, but if you compact you will need 20 to 30% more material.

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