Shotgun Shot Pattern Calculator
Calculate shotgun pellet spread at distance.
Find pattern diameter and pellet density for different chokes and shot sizes.
Pattern Diameter
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