Calculate rise, slope percentage, and grade for drainage and process piping.
Pipe grade is the slope of a horizontal pipe expressed as a percentage, ratio, or angle, critical for gravity drainage, sanitary sewers, sloped condensate returns, and any line that must self-drain. This calculator converts between the three forms and helps verify that a layout meets the minimum slope required to prevent solids deposition or vapor lock.
Grade (percent) = (rise / run) × 100, equivalent to slope = rise / run as a ratio or angle = arctan(rise / run) in degrees. Drainage standards: building sanitary 1% (1 in 100, 5.7° below horizontal, or 0.6°), storm drain 0.5–1.0%, condensate return 1–2%, hydraulic return 0.2–0.5% for self-bleeding. Below 1% slope, solids may settle; above 4% in sanitary lines, water races ahead of solids leaving them behind (also a problem). The calculator returns rise in mm given run in meters, rise in inches given run in feet, and the equivalent angle in degrees.
A plumber laying 30 m of 100 mm DWV at 1% gets rise = 300 mm over the run, marks the slope at each hanger, and confirms the line falls into the main with the proper sub-slope per code.
A facility engineer auditing an old steam plant measures actual fall on a condensate return: 25 mm over 8 m = 0.31% — below the 1% minimum, so the slope is corrected with a redo of the support struts.
A hydraulic-power-unit installer ensures the return line falls 0.3% back to tank so air bubbles travel back rather than pocketing under valve blocks, eliminating intermittent jerky cylinder motion.
Most plumbing codes specify minimum 1% (1 in 100) for 3-inch and smaller; 2% (1 in 50) for 1.25-inch and smaller. International codes vary — confirm with the local authority.
In sanitary lines, above ~4% slope water flows faster than solids, leaving deposits behind. Drainage codes specify both minimum AND maximum slope for waste pipes.
angle (deg) = arctan(percent / 100). 1% = 0.573°, 2% = 1.146°, 5% = 2.862°. For small percent the angle in degrees is roughly 0.6 × percent.