# How many square yards of soil do I need for my planter?
**URL:** https://boards.straightdope.com/t/how-many-square-yards-of-soil-do-i-need-for-my-planter/339983
**Category:** Factual Questions
**Created:** [January 14, 2006, 6:51pm UTC](https://boards.straightdope.com/t/how-many-square-yards-of-soil-do-i-need-for-my-planter/339983 "2006-01-14T18:51:25Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@Mangosteen](https://boards.straightdope.com/u/Mangosteen)
#### Post date: [January 14, 2006, 6:51pm UTC](https://boards.straightdope.com/t/how-many-square-yards-of-soil-do-i-need-for-my-planter/339983/1 "2006-01-14T18:51:25Z")
I’m building a large raised bed planter. Its 25 feet long and 18 inches high, BUT its 16 feet wide at one end and gradually narrows down to 4 feet at the other end. I need to order top soil for it by the square yard.
Is there anyone out there that would know the mathematical formula to answer this question?
Your reply will be greatly appreciated!
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### Author:  [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)
#### Post date: [January 14, 2006, 7:12pm UTC](https://boards.straightdope.com/t/how-many-square-yards-of-soil-do-i-need-for-my-planter/339983/2 "2006-01-14T19:12:44Z")
1. Convert all your units to yards
2. Find the area of the trapezoid formed by the planter walls
3. Multiply the result by the depth of the planter to find the total volume
If this isn’t a homework problem, you’ll want to add some extra for compaction; 10 percent or so ought to do. Also, you’ll want to allow for drainage, so fill the bottom with crushed stone, covered with sand or coarse gravel.
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### Author:  [@enipla](https://boards.straightdope.com/u/enipla)
#### Post date: [January 14, 2006, 7:40pm UTC](https://boards.straightdope.com/t/how-many-square-yards-of-soil-do-i-need-for-my-planter/339983/3 "2006-01-14T19:40:12Z")
Easy, double the size of it then divide by 2.
4 x 25 x 16 = 20 x 25 = 500 sq. (whatever) / 2 = 250 sq. (whatever)
Consider a planter bed the exact same size as the one you have. Lay it next to it. Make a square out of it. That makes it 20 X 25 = 500 / 2 = 250.
250 square feet x 1.5 (18 “) = 375 cubic ft / 27 = 13.8 yards.
You’re going to need a wheel barrow, and some friends. Beer and pizza too.
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### Author:  [@Fish](https://boards.straightdope.com/u/Fish)
#### Post date: [January 14, 2006, 7:44pm UTC](https://boards.straightdope.com/t/how-many-square-yards-of-soil-do-i-need-for-my-planter/339983/4 "2006-01-14T19:44:18Z")
Nine yards, obviously. Your planter, which was just built, is the origin of the phrase “the whole nine yards.”
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### Author:  [@Xema](https://boards.straightdope.com/u/Xema)
#### Post date: [January 14, 2006, 7:47pm UTC](https://boards.straightdope.com/t/how-many-square-yards-of-soil-do-i-need-for-my-planter/339983/5 "2006-01-14T19:47:08Z")
> [@Mangosteen](#):
>
> I need to order top soil for it by the square yard.
You probably mean cubic yard (as enipla implies).
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### Author:  [@AskNott](https://boards.straightdope.com/u/AskNott)
#### Post date: [January 14, 2006, 10:45pm UTC](https://boards.straightdope.com/t/how-many-square-yards-of-soil-do-i-need-for-my-planter/339983/6 "2006-01-14T22:45:56Z")
When you get your cubic yardage carefully calculated, the soil will be precisely measured by the cubic-yard bucket of a payloader tractor. There’s a bit of a fudge factor in that. 😉