How this instrument works
This instrument compares your maximum reach (standing reach plus vertical leap) against rim height in two ways. First, it reports margin — simply how far above or below the rim your maximum reach lands. Second, and more usefully, it answers a stricter question: can you actually dunk? That check subtracts a clearance figure from your reach before comparing it to the rim, because getting the ball above the rim by a fraction of an inch is not the same as controlling it through the hoop with authority.
The standard rim height in the NBA, FIBA, and virtually every organised level of basketball is 10 feet, or 120 inches — a figure that traces back to James Naismith's original 1891 game, where the peach-basket goals happened to be hung from a gymnasium balcony rail that stood exactly 10 feet up. That accidental height became the permanent standard and has never changed since, even as the athletes playing above it have grown taller and jumped higher.
Clearance is the instrument's way of encoding 'dunking, not just touching.' A default of 6 inches means your hand (and the ball) needs to clear the rim by roughly half a foot after accounting for the ball's own size and the control needed to bring it down through the hoop rather than just flicking it over the front edge. Raise the clearance figure for a stricter, more conservative answer; lower it if you're comfortable calling a bare graze a dunk.
- Enter Standing reach — flat-footed, arm fully extended overhead, fingertip to floor, in inches.
- Enter Vertical leap — your maximum jump reach minus your standing reach, in inches.
- Enter Rim height — 120 inches (10 feet) for a standard hoop; lower it for a youth or reduced-height rim.
- Enter Clearance needed — how far above the rim your hand must get to count as a real dunk, not just a touch; 6 inches is a reasonable default.
- Read Margin (how far above or below the rim your reach lands) and Can dunk? beneath the inputs.
Worked example — 100 in reach, 30 in vertical, 120 in rim
Enter 100 inches for Standing reach, 30 inches for Vertical leap, 120 inches for Rim height, and the default 6 inches for Clearance. Maximum reach is 100 + 30 = 130 inches, 10 inches above the 120-inch rim, so Margin reads 10.00.
For the stricter dunk check: 100 + 30 − 6 = 124, which is still at or above the 120-inch rim, so Can dunk reads 1 (yes). Both numbers agree here because the margin (10 inches) comfortably exceeds the 6-inch clearance buffer — there's real room to spare, not just a technical pass.
Questions
How do I measure my standing reach accurately?
Stand flat-footed against a wall or under a doorframe, extend one arm straight up as high as it will go without rising onto your toes, and mark or measure the fingertip height from the floor. Standing reach is typically about 1.33 times a person's height, but measuring it directly is far more accurate than estimating it from height alone.
How do I find my vertical leap for this calculator?
Vertical leap here means your maximum jump reach (fingertip height at the top of your best jump) minus your standing reach — not your total jump height off the ground. A common way to measure it is a standing vertical jump test against a marked wall or jump board, then subtracting your standing reach from the highest mark touched.
Why does the calculator subtract a clearance buffer instead of just checking reach against rim height?
Because barely touching the rim with a fingertip isn't a dunk — a real dunk needs the hand, and the ball, to get meaningfully above the rim so it can be brought down through the hoop with control rather than just flicked over the front edge. The clearance figure (6 inches by default) encodes that difference; raise it for a stricter standard, lower it if you're comfortable calling any contact above the rim a dunk.
Is the rim always 120 inches (10 feet)?
That's the standard for the NBA, FIBA, and nearly all organised adult basketball, and it's the instrument's default. Many youth and lower-level hoops are set lower — 8 feet (96 inches) and 9 feet (108 inches) are common reduced heights — so change the Rim height field to match whatever hoop you're actually measuring against.
What does a negative margin mean?
A negative margin means your maximum reach falls short of the rim entirely — you cannot touch the rim, let alone dunk on it. In the second reference scenario for this instrument, a 90-inch standing reach plus a 20-inch vertical leap reaches only 110 inches against a 120-inch rim, a margin of −10, well short in both the margin and the stricter can-dunk checks.