Shotgun Shot Pattern Calculator
Calculate shotgun pellet spread at any distance.
Find pattern diameter and pellet density for different choke constrictions in clay and sport shooting.
A shotgun fires hundreds of small pellets in a spreading pattern. The pattern diameter at a given range determines the effective area and how many pellets hit the target.
Pattern spread: Pattern diameter (cm) ≈ range (m) × spread factor × choke modifier
Where the base spread factor for a cylinder bore is approximately 2.5 cm per metre.
Choke constriction and spread factors:
- Cylinder (no choke, IC = 0): full spread (~2.5 cm/m)
- Improved Cylinder (IC): ~2.1 cm/m
- Modified (M): ~1.7 cm/m
- Improved Modified (IM): ~1.4 cm/m
- Full Choke (F): ~1.1 cm/m
Pellet count by shot size:
| Shot Size | Pellet Count per oz (28g) | Pellet Diameter |
|---|---|---|
| #9 | ~585 | 2.0 mm |
| #7.5 | ~350 | 2.4 mm |
| #6 | ~225 | 2.7 mm |
| #4 | ~135 | 3.3 mm |
| #2 | ~87 | 3.8 mm |
| BB | ~50 | 4.6 mm |
Pattern efficiency: A good hunting pattern puts at least 70% of its pellets inside a 30-inch (76 cm) circle at the intended range. Most modern guns with full choke achieve this at 40 yards (37 m).
Effective ranges for hunting:
- Upland birds (#6–#7.5): 20–40 yards
- Waterfowl (#2–BB): 30–50 yards
- Turkey (tight patterns): 30–50 yards
- Deer slugs: 75–100 yards
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
SuperGlobalCalculator is independently built and maintained. See how we build and verify our calculators.