Wind is the hardest variable in long-range shooting because it changes the bullet’s sideways position continuously through its flight. This calculator uses the classic lag-time model to turn a wind call into a precise windage hold in inches, MOA, and MIL at every distance you care about.
How it works
Wind drift is driven by lag time — how much longer the bullet takes to reach the target than it would in a vacuum:
time_of_flight = range / average_velocity (approx, drag-corrected)
vacuum_time = range / muzzle_velocity
lag_time = time_of_flight - vacuum_time
drift (ft) = crosswind_speed (ft/s) × lag_time (s)The crosswind component is wind_speed × sin(angle), so a full-value 3 o’clock wind
uses the whole wind speed while an oblique wind uses only part of it. Velocity at range
is estimated from the G1 ballistic coefficient using a retardation approximation, which
captures how the bullet slows down and the wind gains more time to act.
Wind clock value by angle
The angle of the wind relative to your firing line is critical. Use the clock-value multiplier to find the effective crosswind:
| Clock position | Examples | Value | Multiplier |
|---|---|---|---|
| 3 or 9 o’clock | Dead crosswind | Full | 1.0 |
| 2, 4, 8, or 10 | Oblique cross | Half | ~0.5 |
| 1, 5, 7, or 11 | Slight angle | Quarter | ~0.25 |
| 12 or 6 | Head or tailwind | Zero | 0.0 |
For example, a 15 mph wind from 10 o’clock has an effective crosswind of roughly 7.5 mph for the drift calculation.
Converting to a scope hold
Once drift is known in inches at a distance, the angular hold is:
- MOA = drift_inches / (1.047 × range_in_hundreds_of_yards)
- MIL = drift_inches / (3.6 × range_in_hundreds_of_yards)
Most modern precision rifle scopes adjust in either 0.25 MOA or 0.1 MIL clicks. Enter your scope unit when recording dope to avoid unit-mix errors in the field.
Worked example
A rifle shooting a 175-grain .308 bullet at 2,600 fps MV with a G1 BC of 0.505, in a full-value 10 mph crosswind, will drift roughly:
- 200 yards: about 2 inches — less than 1 MOA, sometimes acceptable at this range
- 400 yards: roughly 8–9 inches — about 2 MOA
- 600 yards: roughly 18–22 inches — approaching 3.5–4 MOA, significant
These are illustrative figures; the calculator gives you the exact number for your specific round, velocity, and BC.
Reading wind in the field
The calculator gives you the math; reading the wind correctly in the field is a separate skill:
- Mirage (heat shimmer visible through a spotting scope) reveals the wind near the target, which is often different from the wind at the firing line. Mirage that “boils” vertically indicates a calm.
- Vegetation, flags, and dust near the target tell you the prevailing direction. A flag at 45° extension is roughly half-value; fully extended is full-value.
- Wind often changes faster at the firing line than at mid-range. Shooting in lulls — moments when the wind steadies — reduces shot-to-shot variation and makes your dope more consistent.
Treat the calculator output as your starting hold and refine with observed first-round impacts. All real wind-drift figures assume the wind is constant across the range, which is rarely true; guard against over-correcting on a variable wind.