Measure a ramp slope with your phone or compute it from the rise, then check it against the sizing tables of Brazil's NBR 9050, with segments and landings.
The rule everyone remembers from NBR 9050 is the 8.33 % ceiling, or 1:12. What usually escapes notice is that the standard does not treat slope as an isolated number: it pairs each slope band with a maximum rise that a single ramp segment may overcome, and with a maximum number of segments. Table 4 has three bands. Up to 5 % a segment may climb 1.50 m with no limit on the number of segments. Above 5 % and up to 6.25 % the segment drops to 1.00 m, still with no count limit. And above 6.25 % up to the 8.33 % ceiling a segment climbs at most 0.80 m, with a maximum of fifteen segments. That last figure is the one most often wrong in online calculators, which frequently repeat 1.00 m where the standard says 0.80 m. A second table exists for exceptional situations, which the standard admits only in renovations and only once the possibilities of fully meeting the first have been exhausted. It allows reaching 12.5 %, but at a severe cost: between 8.33 % and 10 % a segment climbs only 0.20 m, and above that just 0.075 m, in a single segment. In practice this confines Table 5 to step-height differences rather than access ramps. Landings sit between segments, at least 1.20 m along the direction of travel, and they are also required at the start and the end. Adding everything up, a ramp near the slope limit usually ends up considerably longer than the naive rise-divided-by-slope arithmetic suggests, because each landing adds length without climbing any height at all.
These references help contextualize formulas, standards, APIs and limitations used on this page. They do not replace professional validation when a result has legal, financial, medical or operational impact.
Under normal conditions, 8.33 %, which is a 1:12 ratio. That is the ceiling of Table 4 and applies to new construction. In renovations, where meeting that table is demonstrably impossible, Table 5 allows up to 12.5 %, but with per-segment rises so small that in practice it only serves to overcome isolated steps.
Rest the device flat on the ramp surface, aligned with the direction of travel, and tap Save reading. For better accuracy, calibrate the device first on the bubble level.
Tap to turn on the accelerometer. Everything is measured on your device and nothing is sent over the internet.
Values transcribed from ABNT NBR 9050:2020, corrected version of 25 January 2021, section 6.6. This tool helps check sizing and does not replace a design signed by a qualified professional or reading the full standard.
Everything is computed in your browser. No measurement, design dimension or sensor reading leaves your device.