Ghost and Montmorency have the correct math. I use excel where the formula is:
Where F2 is vertical and E2 is horizontal length.
I’m curious how people are measuring the vertical and horizontal values. I have tried two methods both leveraging Google earth:
1. Draw a line (path function at top of screen)
2. In the properties box you can get the horizontal length in feet.
3. Two options for vertical measurement:
a. Zoom in to the endpoints, put your mouse on each endpoint and record the elevation of each. Subtract these numbers and you have the vertical component.
b. Zoom into the endpoints and view the value on a topo map overlay. (national geographic has a free topo overlay based on the USGS survey) Ideally with this method, you put the endpoints of the line right on the topo contour lines.
I’ve found such approaches to be fairly accurate as long as the vertical is 100’ or more. The approach does have its limits though including (but not limited to):
+Google earth elevation data isn’t perfect. Google keeps there method a secret but it appears to be based on USGS data and radar data from satellites. The radar data gets thrown off by tall structures (buildings, trees, radio tower, etc) All data appears to be averaged. End result, the steeper slopes are likely to be undervalued and all measurements will suffer some error.
+USGA topo map data is more precise but it is only at 40’ intervals with the contour lines being low resolution. Such limits introduce error, especially for shorter measurements.
+Google clearly has some errors in their data/tools. Big ditches where there isn’t one, the summit appears downhill in Google, etc.
+All measurements neglect snow loading effects.
+All measurements are average angle. A run could be an unskiable cliff or a short very steep chute followed by a flat spot. These short distance effects are not measurable with either measurement approach.