How do I determine ‘closed angle’ and ‘open angle’ of a cover?

Filling in the Cover angle ‘closed angle’ and ‘open angle’ (Start angle and End angle)

The following agreements – in accordance with the hour hand of the clock – apply here:

  • 12 hours on the clock =  90 degrees …. cover stands right up
  • 3 hours on the clock  =     0 degrees ….. cover lies horizontally ……………..’Lying’ Cover
  • 6 hours on the clock  = – 90 degrees …. cover hangs down vertically ….. ‘Hanging’ Cover

Left part of the page: Cover positions such as those which could occur with a ‘Lying’ Cover:

  • Roof hatch (skylight)
  • Attic hatch
  • Toy box
  • Basement hatch
  • Garden box
  • Hatch cover
  • etc.

Right part of the page: Cover positions such as those which could occur with a ‘Hanging’ Cover:

  • Sales vehicle hatch
  • Takeaway counter hatch
  • Sun shading
  • Safety screen
  • Awning on horse trailer/handyman bus
  • etc.

FAQ Rekentool -2- Hoe bepaal ik 'hoek dicht' en 'hoek open' van een klep

* Cover rotates from Start angle to End angle (length of gas spring is then at a maximum)

The intermediate Cover angles can be determined, for example, with an inclinometer or by means of a smart phone (with an inclinometer app).


Do not just accept the inclinometer or smartphone reading as the actual cover angle.

But first, determine the difference between Cover position and horizontal or between Cover position and vertical and then calculate the actual Cover angle from those according to the aforementioned statement.

Cover angles can also be determined by measuring and calculating.

In what ways can such a measurement be carried out and how the calculation is then done, is illustrated in the following examples:

A = inclination of the Cover measured from horizontal (or measured from vertical in another example)

S = Hinge side of the Cover

L = Length of the Cover

Calculating a Cover angle:

  • search on Google for: 1+1                                               –> Google shows a calculator
  • press on the button ‘Rad’                                                    –> a button ‘Deg’ appears
  • press on the button ‘Inv’ and after on the button ‘sin’
  • key the inclination in with the mouse                            –> for example: 3 .. 0 .. 8
  • press the key with the division sign
  • key in the Length of the Cover with the mouse –> in this example: 9 .. 0 .. 0
  • finally press the button‘=’

The result is the inclination of the Cover with respect to horizontal or with respect to vertical (depending on the method of measurement) The result: 20.01 -> rounded up by 20 degrees, we convert to the Cover position: 0 degrees – 20 degrees = 20 degrees
For the Cover position in the example drawn beside it we find: -90 degrees – 15 degrees = -105 degrees

Tip! First copy the calculation from the example so you know whether you have understood the process well.

Posted in: Calculation