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# Math Question

## Math Question

This is for those who like math.

Question #1:

I have 6.75 cubic feet of homemade compost. I have 150 sq. ft. that will need 2" of compost in the next few months.

Question #2:

The tumbler holds 80 gallons which results in about half that amount of usable compost.

Question #1:

I have 6.75 cubic feet of homemade compost. I have 150 sq. ft. that will need 2" of compost in the next few months.

__How much compost__will I need to make to top all of the 150 squares?Question #2:

The tumbler holds 80 gallons which results in about half that amount of usable compost.

__How many batches__will I have to make to have enough compost for the above bed amending?**sanderson****Forum Moderator Certified SFG Teacher**- Posts : 17037

Join date : 2013-04-21

Age : 70

Location : Fresno CA Zone 8-9

## Re: Math Question

Oh, Sanderson... You're not nice, trying to make me think this early in the morning! And MATH at that.... ;-)

**AtlantaMarie***Certified SFG Instructor*- Posts : 4791

Join date : 2014-03-18

Age : 55

Location : Buford, GA - Zones 7B/8A

## Re: Math Question

Question #1: 21.25 cubic feet.

You will need a total of 25 cubic feet for 150 sq ft at 2" depth. Since you already have 6.75 cubic feet, you need an additional 21.25 cubic feet. Calculated using this compost calculator and then double-checked with this more confusing compost calculator

Question #2: 4 batches

You need 21.25 cubic feet, which is about 137 gallons. Since you're getting about 40 gallons per batch, you'll need 3.425 batches, or a "real world" total of 4 batches. Conversion using this conversion calculator

Please double-check my figures before accepting these answers. I've not had my full pot of coffee yet!

Thanks for exercise - I love word problems

You will need a total of 25 cubic feet for 150 sq ft at 2" depth. Since you already have 6.75 cubic feet, you need an additional 21.25 cubic feet. Calculated using this compost calculator and then double-checked with this more confusing compost calculator

Question #2: 4 batches

You need 21.25 cubic feet, which is about 137 gallons. Since you're getting about 40 gallons per batch, you'll need 3.425 batches, or a "real world" total of 4 batches. Conversion using this conversion calculator

Please double-check my figures before accepting these answers. I've not had my full pot of coffee yet!

Thanks for exercise - I love word problems

**BlackjackWidow**- Posts : 173

Join date : 2018-05-07

Age : 56

Location : SW Michigan, on the coast of Lake MI; Zone 6a/b

## Re: Math Question

BJW,

Your mathematical total approximates my rule of thumb:

To top off one 4' x 4' requires approximately one cubic foot of compost (1" deep).

There are approximately 10 such beds in this example. Therefore, 2" would require approximately 21 cubic feet.

Your mathematical total approximates my rule of thumb:

To top off one 4' x 4' requires approximately one cubic foot of compost (1" deep).

There are approximately 10 such beds in this example. Therefore, 2" would require approximately 21 cubic feet.

**donnainzone5***Certified SFG Instructor*- Posts : 2287

Join date : 2010-03-02

Age : 71

Location : Bend, OR (Zone 5-6)

## Re: Math Question

I should have added the following information. I am using the conversion value of 8 gallons/cubic foot.

**sanderson****Forum Moderator Certified SFG Teacher**- Posts : 17037

Join date : 2013-04-21

Age : 70

Location : Fresno CA Zone 8-9

## Re: Math Question

@sanderson wrote:

I should have added the following information. I am using the conversion value of 8 gallons/cubic foot.

Hmmm. OK, the site I used said 6.25 gallons = 1 cubic foot. Using your conversion doesn't change the amount needed. Thanks SO MUCH for the confirmation, donnainzone5! So... at 8 gals/1 cuft 21.25 cubic feet = 170 gals. Still at 40 gals/batch... 170 divided by 40 equals 4.25.

So... not much change. Basically, a little more than 4 batches. Or round up to 5 and have 3/4 batch left over.

I think I have a headache... lol

**BlackjackWidow**- Posts : 173

Join date : 2018-05-07

Age : 56

Location : SW Michigan, on the coast of Lake MI; Zone 6a/b

## Re: Math Question

BJW,

Well, I used to be able to count in my sleep. I should say, count and convert to the values in Thorp's strategy tables.

If ingredients are labeled by the gallon, it seems the only conversion needed is gallons = ? cubic feet.

Actually, math was my worst subject, beginning with Algebra. The basics were simple.

I hope my rule of thumb is useful here.

Well, I used to be able to count in my sleep. I should say, count and convert to the values in Thorp's strategy tables.

If ingredients are labeled by the gallon, it seems the only conversion needed is gallons = ? cubic feet.

Actually, math was my worst subject, beginning with Algebra. The basics were simple.

I hope my rule of thumb is useful here.

**donnainzone5***Certified SFG Instructor*- Posts : 2287

Join date : 2010-03-02

Age : 71

Location : Bend, OR (Zone 5-6)

## Re: Math Question

A cubic foot is 7.48 gallon. Rounded 7.5 gal. Hence 3 five gallon pails give you 2 cubic feet.

at 2 inches deep, each cubic foot covers 6 squares. 150/6 = 25 cubic feet before settling. 25 - 6.75 = 18.25 cubic feet needed. 18.25 × 7.5 = 136.875 gallins. Round to 137 or 140. 140/40 = 3.5 so four batches.

at 2 inches deep, each cubic foot covers 6 squares. 150/6 = 25 cubic feet before settling. 25 - 6.75 = 18.25 cubic feet needed. 18.25 × 7.5 = 136.875 gallins. Round to 137 or 140. 140/40 = 3.5 so four batches.

**No_Such_Reality**- Posts : 627

Join date : 2011-04-22

Location : Orange County, CA aka Disneyland or Sunset zone 22

## Re: Math Question

And, we have a winner! NoSuchReality

1. 150 squares covered with 2" of compost.. 2" of compost is 1/6th of a cubic foot. 150/6 = 25 cu. ft. needed.

2. I have 6.75 cu. ft. 25.0 - 6.75 = 18.25 cu. ft. need to be made.

3. Using 7.5 as NSR did, 18.25 x 7.5 = 137 gallons need to be made.

4. 137 gallons needed / 40 gallons per batch = 3.425 batches, so 4 batches.

1. 150 squares covered with 2" of compost.. 2" of compost is 1/6th of a cubic foot. 150/6 = 25 cu. ft. needed.

2. I have 6.75 cu. ft. 25.0 - 6.75 = 18.25 cu. ft. need to be made.

3. Using 7.5 as NSR did, 18.25 x 7.5 = 137 gallons need to be made.

4. 137 gallons needed / 40 gallons per batch = 3.425 batches, so 4 batches.

**sanderson****Forum Moderator Certified SFG Teacher**- Posts : 17037

Join date : 2013-04-21

Age : 70

Location : Fresno CA Zone 8-9

## Re: Math Question

Donnain - "count and convert to the values in Thorp's strategy tables"

I type lol a lot, but this time I literally laughed out loud. Nearly spit coffee on my monitor!

I type lol a lot, but this time I literally laughed out loud. Nearly spit coffee on my monitor!

**couldn't find a way to edit my original post, so I deleted and re-posted. Reason for editing: post to Sanders sounded too sarcastic. Hard to properly show emotions sometimes***BlackjackWidow**- Posts : 173

Join date : 2018-05-07

Age : 56

Location : SW Michigan, on the coast of Lake MI; Zone 6a/b

## Re: Math Question

I've done that a few times on this Forum!

**sanderson****Forum Moderator Certified SFG Teacher**- Posts : 17037

Join date : 2013-04-21

Age : 70

Location : Fresno CA Zone 8-9

## Re: Math Question

Sanderson needs 4 more batches of compost. A brand new one is cooking in the tumbler. How many more batches does Sanderson need to make?

**sanderson****Forum Moderator Certified SFG Teacher**- Posts : 17037

Join date : 2013-04-21

Age : 70

Location : Fresno CA Zone 8-9

## Re: Math Question

15,323? :-)

**AtlantaMarie***Certified SFG Instructor*- Posts : 4791

Join date : 2014-03-18

Age : 55

Location : Buford, GA - Zones 7B/8A

## Re: Math Question

Close, or at least it seems that way.

**sanderson****Forum Moderator Certified SFG Teacher**- Posts : 17037

Join date : 2013-04-21

Age : 70

Location : Fresno CA Zone 8-9

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