Slope Calculator 2026

Slope in percent = (height difference / horizontal distance) × 100. Example: With 8 cm height difference over 4 m distance, the slope is (8 / 400) × 100 = 2%. Both values must be in the same unit (here cm).

Slope in percent is the ratio of height difference to horizontal distance × 100. Degrees measure the actual angle between the inclined surface and the horizontal. The conversion is: angle = arctan(slope% / 100). A 2% slope equals only about 1.15° — for small slopes, percent and degree values are nearly identical.

For terraces and balconies, DIN 18531 recommends a slope of 1.5% to 2.5% — ideally 2%. This means: Over 1 meter length, the surface drops 2 cm. The slope should always direct away from the building so that rainwater drains reliably and no standing water forms.

For a drainage pipe with nominal diameter DN100 (the standard in households), the minimum slope is 1.5% per DIN EN 12056. This means: Over 1 meter of pipe length, the pipe must drop at least 1.5 cm. Smaller pipes (DN50) require at least 2.5%, larger pipes (DN200) only 0.5%.

Place a 2 m spirit level (or straightedge) on the surface. Lift one end until the bubble is centered. Measure the gap between the lifted end and the surface in mm. At 2% slope, the gap is exactly 40 mm over 2 m. Formula: Slope % = gap (mm) / length (mm) × 100.

A slope of 1:50 means the surface drops 1 unit over 50 units of length. This equals 2% slope (1/50 × 100 = 2%). In other words: over 1 meter, the surface drops 2 cm. This notation is commonly used in construction plans.

Key DIN standards: DIN 18531 (terraces/balconies: 1.5-2.5%; flat roofs: 2-5%), DIN 18534 (walk-in showers: 1.5-2%), DIN EN 12056 (drainage pipes: depends on diameter), DIN 4095 (drainage: 0.5-2%), DIN 18040-1 (wheelchair ramps: max. 6%).

Per DIN 18040-1, a wheelchair ramp may have a maximum gradient of 6%. The ramp must not exceed 6 m in length, after which an intermediate landing of at least 1.50 m is required. Minimum width is 1.20 m. Stricter requirements may apply outdoors (max. 4%).

Height difference (cm) = slope (%) / 100 × distance (m) × 100. Example: At 2% slope over 5 m: 2/100 × 5 × 100 = 10 cm height difference. Our calculator has a dedicated mode for this.

With insufficient slope, water cannot drain properly. On terraces, puddles form leading to frost damage and algae growth. In pipes, solids accumulate causing blockages. On flat roofs, standing water can damage the waterproofing. Insufficient slope is one of the most common causes of building damage.