Degree–Percent Slope Conversion
Slope is expressed in three different units: degrees, percent and millimetres per metre. At small angles the percent slope is about 1.75 times the degree value; 1° means about 1.75% and a deviation of about 17.5 mm per metre. You need to know this conversion when comparing a manual's tolerance with a device reading.
Percent slope is a hundred times the ratio of the vertical difference to the horizontal distance: slope % = 100 × tan(angle). Because the tangent is very close to the angle at small angles, a practical shortcut can be used.
- 1° ≈ 1.75% ≈ 17.5 mm per metre
- 0.5° ≈ 0.87% ≈ 8.7 mm per metre
- 0.1° ≈ 0.17% ≈ 1.7 mm per metre
- 3° ≈ 5.24% ≈ 52 mm per metre
This conversion is useful in two places. First, equipment manuals sometimes give the tolerance in degrees and sometimes in percent; you cannot say you are within tolerance without converting both to a common unit. Second, to make a numerical degree concrete: on a caravan 5 metres long, a deviation of 0.5° is about 44 mm end to end, that is, more than the thickness of a finger. A number that looks small on the levelling display is not small at all once multiplied by the body length.
Context in which this term is used: RV automatic levelling guide