Basketball Size Chart: Ball Sizes by Age & League 2026

The right ball is the one the player can control

A basketball is sized by its circumference — the distance around the ball. The full-size ball, Size 7, is 29.5 in around and 9.39 in across, and weighs 22 oz (624 g). A 12-year-old boy plays with a Size 6 — 28.5 in around, 9.07 in across, 20 oz (567 g) — and moves up to Size 7 at age 15. A ball that feels too big is the wrong size even if the age fits — try the next size down.

Basketball size chart — size, circumference, diameter, weight, ages, used by

Every diameter cell is circumference / pi to 2dp, half-up, and every grams cell is ounces × 28.349523125 to 0dp, half-up — derived from the size value, never hand-typed. A ROUNDED diameter back-converted to circumference overshoots by a hundredth: 28.49 in for Size 6 (exact 28.5 in), 25.51 in for Size 4 (exact 25.5 in), 21.99 in for Size 3 (exact 22.0 in). The table’s circumference column is the EXACT official value; the diameter column is C/pi to 2dp — never "correct" 28.49 to 28.50 or 25.51 to 25.50. Check the identities: diameter = circumference / 3.14159265; grams = ounces × 28.349523125. At the defaults — age 12, male — the recommended size is Size 6 (28.5 in, 9.07 in, 20 oz / 567 g), and the next size up is Size 7 at age 15.

The worked example, line by line

Setup: age 12, male.

Line 1 — the age rule. 12 falls in the 12–14 band, so the size is Size 6.

Line 2 — the circumference. The official circumference for Size 6 is 28.5 in.

Line 3 — the diameter. 28.5 / 3.14159265 = 9.07 in.

Line 4 — the weight. 20 oz × 28.349523125 = 567 g.

Line 5 — the next size up. Size 7 starts at age 15.

Reverse: the diameter for a 29.5 in circumference is 9.39 in (exact 9.3901 in). The circumference for a 9.39 in diameter is 29.50 in (exact 29.4996 in). The first age for Size 7 (male) is 15 (at 14 the pick is Size 6). The first age for Size 5 is 9 (at 8 the pick is Size 4). The weight in grams for Size 6 is 567 g (exact 566.9905 g). The weight in ounces for 482 g is 17.00 oz (exact 17.0020 oz).

Every branch, checked

Age 8, male: Size 4 (25.5 in, 8.12 in, 14 oz / 397 g), next size up Size 5 at age 9. An 8-year-old plays Size 4 — the 5–8 band.

Age 16, male: Size 7 (29.5 in, 9.39 in, 22 oz / 624 g). A 16-year-old boy plays the full-size ball — Size 7, 29.5 in around.

Age 16, female: Size 6 (28.5 in, 9.07 in, 20 oz / 567 g). A 16-year-old girl plays Size 6 — women stay on Size 6 at every adult age.

Age 4, male: Size 3 (22.0 in, 7.00 in, 10 oz / 283 g), next size up Size 4 at age 5. A 4-year-old plays the smallest ball — Size 3, the first ball.

Age 10, male: Size 5 (27.5 in, 8.75 in, 17 oz / 482 g), next size up Size 6 at age 12. A 10-year-old plays Size 5 — the 9–11 band.

Age 14, female: Size 6 (28.5 in, 9.07 in, 20 oz / 567 g). A 14-year-old girl plays Size 6 — the 12–14 band, and she stays on it.

What the defaults assume

The model assumes the standard youth progression (under 5 → Size 3; 5–8 → Size 4; 9–11 → Size 5; 12–14 → Size 6; 15+ male → Size 7; 15+ female → Size 6) and the official Spalding/NBA/WNBA circumferences. It assumes the diameter is circumference / pi and the grams are ounces × 28.349523125, both rounded half-up. At age 0 the pick is Size 3 — any ball works, so the smallest is the pick. At age 100, male, the pick is Size 7 — the age rule caps at the adult size. At age 5 the pick is Size 4 — the boundary: 5 is the first Size 4 age, 4 is Size 3. At age 15, female, the pick is Size 6 — women stay on Size 6 at every adult age. Rounding convention: totals are computed from unrounded values, so rounded parts may differ by a cent from their rounded sum; the reverses are nearest-value solutions, and the exact unrounded figures (9.3901 in, 29.4996 in, 566.9905 g, 17.0020 oz) are stated wherever the rounded figures appear.

Output · formula · meaning

Who uses this

• The parent buying a first ball for a 4-year-old: they learn the pick is Size 3 (22.0 in, 10 oz) — and they check the age-8 branch (Size 4 (25.5 in, 8.12 in, 14 oz / 397 g), next size up Size 5 at age 9) for the next ball.
• The coach sorting balls for a 12-year-old team: they learn the pick is Size 6 — and they check the 10-year-old branch (Size 5 (27.5 in, 8.75 in, 17 oz / 482 g), next size up Size 6 at age 12) for the younger squad.
• The parent of a 16-year-old girl: they learn the pick is Size 6 — and they check the 16-year-old boy (Size 7 (29.5 in, 9.39 in, 22 oz / 624 g)) to see why the balls differ.
• The player moving up to the adult ball: they learn Size 7 starts at age 15 — and they check the diameter (9.39 in) to feel the difference.

Accuracy & limitations

The math is first-principles geometry: diameter = circumference / pi; grams = ounces × 28.349523125. Every table cell is derived from the size value — the Size 7 diameter is 29.5 / 3.14159265 = 9.39 in, not a hand-typed number. The 4-decimal exact is shown where the rounding matters: the diameter for a 29.5 in circumference is 9.3901 in (shown as 9.39 in); the circumference for a 9.39 in diameter is 29.4996 in (shown as 29.50 in); the weight in ounces for 482 g is 17.0020 oz (shown as 17.00 oz). What the model cannot do is measure YOUR ball: it assumes the official circumferences, and real balls vary a little with inflation and wear — a ball that feels too big is the wrong size even if the age fits, so try the next size down. For running pace, see the running pace chart; for calories burned running, see the calories burned running calculator; for body mass index, see the BMI calculator; and for daily energy needs, see the TDEE calculator. This is a calculator, not coaching advice.