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Cut and Fill Calc's on form•Z

Cut and fill calculations can be a very long and tedious task in any profession. So I have taken the liberty to discover an easier way to accomplish this daunting task. This page will help demonstrate my work with form•Z and how it makes cut and fill calc's a snap.


The Process

This project came about after I had been working with form•Z terrain models in one class (Arch481) while also doing cut and fill calc's in a landscape construction class. In our construction class we learned how to calculate cut and fill using a large grid format along with a formula to calculate change in grade per grid cell. This method was very long, boring and filled with numerous mistakes. So I set out to find an easier way to calculate cut and fill. This page is a look at how form•Z cut and fill calculations compare with those done by hand.

Feel free to download the DXF contour files and try this yourself. I'd appreciate it if you'd e-mail me with your results


Beginning with a Site Plan

The first step in calculating cut and fill is finding a project site that has existing and propsed contours on it. Here is the site I worked with for this project. The dashed lines are the existing contours and the solid lines are the proposed ones.

Site plan of project


Calculating Cut and Fill

I asked around school and at work to see how most landscape architects calculate cut and fill. There were two main answeres: Section Calculations & Area by Volume Calculations. Section Calculations are done by cutting multiple sections through a site to find volume, then multipllying that section by the linear value between those sections to get an overall calculation for each section. This is a very rough estimate at best.

The Area by Volume Method, which also seemed to be the most popular method, is done by calculating the area of each contour, and then multiply that area by the depth of the contour to get an overall cubic footage for each contour. Once you have the cubic footage for each contour, you just add them up to get a total cubic footage for the contours. You do this for both the proposed and Existing contour maps, then subtract the proposed value from the existing value to get a overall value. A total positive value means the site requires that much fill, and a total negative number means that the site requires that much cut. As you can see this is a very time consuming task. Now I'll demonstrate how this task can be accomplished in form•Z at about 1/10th the total time!

Check out my hand calculated numbers


The first step in calculating cut and fill in form•Z, is to take site contours and scan them into the program. Below are the existing and proposed contours from the site shown above.

Existing contours traced in form•Z

Download existing contours

Proposed contours traced in form•Z

Download proposed contours


Creating Terrain Model

Once you have the contours traced into form•Z, you can then create a stepped model of each group of contour lines. This is done by using the Terrain modeling tool in the program. You select the type of model (I used a step model), then you adjust the contour intervals and starting height, then select the contour lines in ascending order and then you have a 3-D step model of your site!!! Below are the steped models fro the existing and proposed contours of my project site.

Existing contours terrain model

Proposed contour terrain model


Comparing Cubic Footage

Once you have the two terrain models (existing and proposed), you can do a query on each of them to see the cubic footage of each model.

Query on exsitng terrain model

Query on proposed terrain model


Final Cut and Fill Calculation

Once you have these numbers, you subtract the proposed number from the existing number to get a total change in cubic footage. This number is used to calculate cut and fill just like the hand done calculation were, meaning that a negative number means overall cut, and a posative number means overall fill. Here are my numbers:

Existing Terrain model =

Proposed Terrain model =

Difference =

257,503.389 cubic Feet

245,786.024 cubic Feet

-11,717.365 cubic Feet


Final Conclusions

Well there you have form•Z's final cut and fill Calculation, but how does it compare to those done by hand. Well lets look at what I came up with:

Final results per Method

Hand calculated using "Area by Volume" Method =

Calculated by form•Z =

About 12,500 cubic feet of Cut

11, 717.365 cubic feet of Cut


As you can see the numbers are very close. But the real key here is the amount of time it took to do each set of calculations. Lets compare those:

Time to calculate per Method

Hand calculations =

form•Z calculations =

approx. 1.5 hours

approx. .5 hours


The bottom line here is that form•Z can can calculate precise cut and fill calculations in about a third of the time it takes to do the same calculations by hand (if you never make simple mathmatical errors I mind you). Therefore I can honestly say that form•Z is a quicker more accurate way of calculating cut and fill, and should be used more readily to save time and money on this annoying task. But, cut and fill is not all form•Z is good for, check out my other pages to see what other aspects of landscape architecture form•Z is a more efficient tool.


Chad Whichers, 1998