Just in case you are trying to fathom out some markings on a plan somewhere….

The Formula is as follows…… degree of slope X 1.746 cm X 1 Metre of run equals rise in centimetres ( or negative FALL)

e.g. (DDO8)  2.5 degrees over an 8 meter span = 2.5   X 1.746 cm X 8 metres = 34.92 Cm per meter, or 0.3492 m  rise, over a meter sideways.

trigonometry rise

The gradient (also known as slope) of a line is defined as:     gradient =  vertical rise  / horizontal run

Say a 2 meter rise, over an 8 meter run is  2/8 = 1/4 = .25m  or could be referred to as “1 in 4.”


  1. Talford says:

    Thanks for the information. I have noticed that most of the planning schemes throughout Melbourne express fall in degrees which is often confused with percentage of gradient. The following condition is included in the Manningham Planning Scheme in regard to building height limit applicable to the DDO8;
    “9 metres, unless the slope of the natural ground level at any cross section wider than eight metres of the building is 2.5 degrees or more, in which case the maximum building must not exceed 10 metres”.
    Using your formula the above is near enough to a fall of .350m in 8m.

  2. Danil says:

    thanx, but very little about roof pitch in degrees

  3. Russ says:

    Nice approximation … but remember it is an approximation. The error increases with angle (-1% error at 10 degrees, -10% error near 30 degrees, -20% error near 45 degrees).

  4. Philip says:

    Is it it 1.74533 which rounds to 1.745 not 1.746! 1 degree in radians =…

  5. Manny Tampakas says:

    Hi we are working on a new build ( house) we have a problem with the sub floor , I was wondering
    If I were able to use this formula?
    We need to find the total slope or fall in mm , or cm , the floor run is 7 mt long
    I have put my iPhone down on the floor in 7 areas starting from left to right and it give me. 1degree
    At approx 1 mt , 2 degree in 2 mt , 3degree in mt ect how do I measure or convert to mm?

    1. Doris Tran says:

      Reg, one of the plumbers working on our house has suggested that if you don’t have access to a dumpy level a line level would be suffice. Just peg out the building footprint and from its highest point fix one end of the line at ground level. You will need some one to help you raise or lower the string line to determine the amount of fall to the lowest point. Any hardware store would have one in stock. If you are not sure you can always ask the store salesman

  6. Andrew Stubbs says:

    I need to get a 1:80 fall over a 2.5m length, what is the fall in mm please

    1. Doris Tran says:

      More detail required… what are you proposing?

    2. rob says:

      1:80 ratio; 2500mm divided by 80 = 31.25mm is this what you were looking for?

  7. Theodoor says:

    i need to build a ramp for a wheel chair.
    total rise 40 cm,

    how long is ramp

    1. Doris Tran says:

      Regulations are 1 in 14. 5.6 m make it 6 m to ensure compliance

  8. Trevor says:

    2.4 high sloped 5 degrees over 4 metres would give me what height at the end of the 4 metres

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