Dunking comes down to one simple gap: the distance between how high you can already reach standing still, and how high the rim sits — plus a little extra so you can control the ball on the way through. This calculator turns that gap into a single vertical-jump number, using your height, an optional measured standing reach, and the rim height you're playing on.
How the Dunk Calculator works
The core formula is vertical needed = rim height + clearance − standing reach. Rim height defaults to the regulation 10 ft (120 in), and clearance defaults to 6 in — a commonly used margin that leaves room to actually control the ball through the hoop rather than just brushing the net.
If you don't enter a standing reach, the calculator estimates one from your height using the widely-cited rule of thumb reach ≈ height × 1.33. This works because arm span averages close to height for most people, so a player's standing reach — height plus roughly half of any arm-span/height difference — tends to land near that multiplier. It's an estimate, not a measurement: two players of the same height can have meaningfully different reaches depending on wingspan.
Inputs and what they mean
Height is your only required input — everything else has a sensible default. Standing reach is optional; leave it blank to use the height-based estimate, or enter a measured value (stand flat-footed, reach one arm straight up, measure fingertip to floor) for a more accurate result. Rim height defaults to 10 ft but can be lowered for youth hoops or backyard setups. Clearance is the input with the biggest swing on the answer relative to its size — moving from 6 in to 2 in of clearance can shave 4+ inches off the vertical you need, so treat a low-clearance result as an optimistic floor, not a guarantee. On the Can I Dunk? tab, your actual vertical jump is compared against the requirement and against common benchmarks (untrained ~16 in, average athlete ~20 in, good athlete ~24 in, elite ~30 in).
Limits and edge cases
This calculator estimates a physical requirement, not a guarantee you can execute it — timing, ball control, hand size, and jumping technique all matter in practice and aren't modeled here. The 1.33x reach estimate is a population average; if your wingspan is unusually long or short relative to your height (check the Ape Index calculator), your actual reach could differ by several inches either way. And a "vertical needed" at or near zero simply means your standing reach already clears the rim + clearance — you'd still need enough of a hop to get the ball fully through with control, even without much air time.