Writing trig equations in Excel

[Aussiebear]

Just recently I've been tasked with calculating slope while conducting dozer operations. Now I understand that 1° slope equals 1m rise in 100m distance, but Mother Nature unkindly does not produce uniform slopes. How do I write this as a "Slope percentage"? Various you tube videos suggest that inverse Tan (Rise / Distance) but I don't have a trig calculator to test this. Excel doesn't seem to provide an Inverse Tan function either that I can find.

A recently downloaded trig calculator when run with the following data 2m Rise, 50m Distance suggests 2.3° for slope, but also suggests the Hypotenuse is 50.0 which I think is incorrect ( unless the value is less than 50.049 and it rounds down).

The only other way I have arrived at is the following formula =((Rise/Distance)*100)/1.76 which seems to work but I am unable to accurately confirm the results with certainty. The 1.76 figure is something that I found quite some time ago to convert Degrees to percentage but I'm also uncertain if this is accurate since Google searches suggest also 1.75.

Since trig calculations seem to work on small distances ( Engineers seems thrive on the damn stuff), can anyone find a way to test if my formula is accurate?

Example: Rise 220m, Distance 1700m. The trig calculator suggests 7.4° and my formula also suggests 7.4° when simplifying the result to one decimal place. Am I on the right track?

[arnelgp]

when you divide rise by distance, what you get is an Angle (in Radian).
to convert it to Degree, multiply the result by 180 and divide th Pi (3.141593):

=rise / distance * 180 / 3.141593

Reference:
Radian to Degree Measure (varsitytutors.com) (https://www.varsitytutors.com/hotmath/hotmath_help/topics/radian-to-degree-measure)

[georgiboy]

Indeed but when checking on some of the websites that do the calculation for you they seem to be using ATAN function:
https://www.to-calculate.com/construction/slope-gradient.php#calculation


=ATAN(Rise/Distance)*(180/PI())

I was trying to work out why the websites were different.

[arnelgp]

yes, you need to use Tan-1 or ATAN (in excel) first before multiplying to 180/3.141593.
the sample in Varsitytutors.com is already in Radian.

[Aussiebear]

Hmmm...

Aussiebear's formula results in 7.3529412
Arnelgp's formula results in 7.4147542
Georgiboy's formula results in 7.3737663


Good thing I'm not building a bridge I guess:wot

[georgiboy]

That clears things up then, just take the average: 7.38048723333333 :rofl:

[Aussiebear]

just checked the trig calculation app and it shows how it arrived at the result. Tan(0)(Rise/Distance).

I would have responded earlier but John Wick Parabellum was on TV

[p45cal]

=DEGREES(ATAN(220/1700))
gives 7.373766 degrees

=DEGREES(ATAN(1/1))
gives 45 degrees, as you'd expect.

Test your other formulae with rise = 1 and distance = 1, you'll soon see which is good.

[Paul_Hossler]

29968

This is the way I'd calculate percent slope

But since you're down under, you'll probably need to take the negative :devil2::rotlaugh::rotlaugh::devil2: (just kidding)



29969

I'm not sure if just checking and using the two end points is accurate. The graph is a bit exaggerated but you get the idea

[georgiboy]

When I tested I checked 3 different websites to see their result as I am no expert on angles tbh:
29965
29966
29967

[Aussiebear]

Thank you one and all I'm convinced with both Georgiboy's and P45cal's versions. Mine in the bin and sadly arnelgp's is as well.