Forest mensuration (measuring trees and forests) has come of age. I have written a few posts about forest mensuration and also how to use a smartphone to measure tree height – see links below. I recently came across some really impressive apps for use by foresters and woodland owners to measure trees and areas, and to calculate stand basal area, using an iPhone smartphone.

The Relascope (Spiegelrelaskop), invented by Austrian forester Walter Bitterlich (1908-2008), is a specialist and expensive instrument used by foresters to estimating tree height, distance to tree (although this is complicated), and the basal area of a stand (the sum of the cross-sectional area of trees, taken as a dbh and calculated inside the bark). Although a superb instrument and highly accurate in trained hands, the Spiegelrelaskop is not likely to be used by many private woodland owners as it is unaffordable to many (£1500/$2400). Other relascope types are available, see How to use a wedge prism relascope to measure basal area, but the development of powerful forest mensuration tools for smartphones, which most people carry today, is very welcome.

The apps that I’ve been trying are available free from the Apple app store, developed by Taakkumn Watakushi from Fukushima  in Japan. I have no hesitation in recommending these two apps as I’m not aware of anything else like these that are available for foresters.  He also provides a compass surveying app (iCompass Surveying) that enables areas to be measured but I have not tested it.

The iHypsometer is a free (in the ‘Lite’ version) tool for estimating tree height. It works on the same principles of trigonometry that I explained in How to measure tree height using a smartphone but it copes with sloping ground (i.e. when the base of tree is not level with your feet) and it completes all the tricky maths for you. It requires that you have a ‘friend’, whose height you should measure, and who should stand next to the tree, although I find that a stick cut to a suitable height works just as well. Angle measurement works in the same way as I described in How to measure tree height using a smartphone except that it uses the short side of the phone. The only feature that I would like the developer to improve is to use the longer side of the phone for sighting along, as I have found in other apps that this provides much greater accuracy.

The iBitterlich is a free app for calculating forest stand basal area. It uses the view from the camera on an iTouch (latest model)/iPhone 3G and up/iPad, on which it overlays buttons where the number of trees of different categories of dbh can be counted simply by pressing them. In the screenshot (below) I was looking at the second tree that I had counted as a ‘+3’, and I had already counted 4x ‘+2’ and 11x ‘+1’ trees in my sweep, that at this point was almost complete at 320 degrees.

iBitterlich iphone app screenshot
iBitterlich iphone app screenshot. This tree is a ‘+3’. Basal area and Stand volume are displayed at the top.

After finishing a 360 degree sweep of the forest stand and counting all the trees, the average tree height is entered in another field, and form factor can be adjusted. The stand volume m3/ha and basal m3/ha are then displayed at the top of the screen. Visit the iTunes app store to download iBitterlich

Have you tried these apps in the forest and did they work for you? Are you aware of similar apps from other developers? Is there a similar set of apps for the Android platform? Do let me and readers know by sharing your views via a comment.

Gabriel Hemery

Other posts about forest mensuration


  1. Beware of putting much faith in any smartphone compass app. Smartphone compass apps are notoriously inaccurate – my own research proves this out. Visit “” to find explicit research related to the accuracy (or lack thereof) specific Android/iPhone compass apps as well as laser rangefinders (with compass). Also, my research proves that the smartphone’s residual (after calibration) azimuth deviation error can be corrected (compensated) quite well. Take a look at
    Fixing Rangefinder & Smartphone Residual Compass (azimuth) Deviation Errors – Android & TruPath Compass app (INTRODUCTION)

  2. Are any of these apps compatible with android

    1. Hi Alex,

      The Cruise Angle iCMT, CMT Forester GPS GIS and Stakeout iCMT apps from cmtinc are for iOS devices only.

  3. Hi Gabriel,

    As many foresters already own an iPhone, it makes sense to take along a few useful apps and leave behind the miscellaneous hardware gadgets. We’ve just released on the App store the Cruise Angle iCMT app that will turn the iPhone, iPod and iPad into an angle gauge for selecting trees for point sampling. This app will let you calibrate your device to obtain an accurate angle-length factor. It will display the tree tally as well as the basal area per acre (or per hectare) for the point cruised. You can select from a list of commonly used BAF values in the English or the metric system. The app comes with functions for calculating limiting distance, leaning tree height and horizontal distance with slope correction. You don’t need a phone signal to work with the cruise angle gauge in this app. Next month we will release our Forester GPS GIS app, which will include this angle gauge plus a load of other functions, such as digitizing an area and creating grid points for point sampling, staking out each grid point and recording the tree tally and basal area information with each grid point, enter deed calls to obtain a deed plot, creating buffer areas, locating a point by its coordinates, and so on. Hardware and software capabilities of modern mobile devices are increasing by leaps and bounds. Perhaps you could write a blog to invite foresters to suggest what they wish their mobile device could do to help them do their job more quickly and easily.

  4. Hi Gabriel,

    As many foresters already own an iPhone, it makes sense to take along useful apps on the device and leave behind the miscellaneous gadgets, books, paper and pencils. We’ve just released on the App Store our Cruise Angle iCMT app, which turns the iPhone, iPod touch or iPad into an angle gauge. This app also provides calculations for limiting distance, leaning tree and slope correction, and will display the basal area per acre (or per hectare) for a point cruised. In addition, you can also measure distances and areas on the displayed Apple Map. This app will work with both the English and the Metric BAF’s and distance/area units. The built-in gauge can be calibrated for each individual iPhone to obtain accurate results for sample tree selection and basal area per acre/hectare computation.

  5. Author

    Hi Rupert and thanks for your comments. I confirm that you don’t need a phone signal as the app functions without one.

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