Adult shoulder height (at the withers) is the standard reference point for this kind of estimate, sourced from field guides and hunting references. Those published figures are the male animal. Female, calf and young-adult figures aren't independently published for most species — females are scaled by a per-species dimorphism band (equal, modest, clear or strong), and calf/young adult by 55% and 90%, based on typical ungulate growth patterns. Anything marked ~ is a derived estimate, not a measurement — treat it as a starting point and check against your own references.
Athlon Argos BTR Gen 2 · 6-24x50 FFP IR MIL — FFP: mils are true at any magnification
Target Inputs
Target height
Mils subtended
mil
Target spans 4.20 mil — drag the lines to match
±5 mil shown
Mil formula (FFP — no magnification term needed)
Because this reticle is First Focal Plane, the mil subtension you read off the reticle is accurate at any zoom setting — no "true magnification" adjustment required.
1
Target height in meters
Hm = 1.5 m
→ H = 1.500 m
2
Solve for distance
D = (H × 1000) ÷ Mils = (1.500 m × 1000) ÷ 4.2
→ D ≈ 357.14 m
Estimated Range
357.1 m
≈ 1172 ft / ≈ 390.6 yd
Reusable formula
D (m) = [ H (m) × 1000 ] ÷ Mils
1 milliradian subtends 1 unit of height at 1000 of that same unit in distance — so keeping H and D in matching units is what makes the formula work. The APMR reticle's hash marks are in 0.5 mil increments, with finer 0.2 mil graduations between 7–9 mil on the stadia lines — estimate your mil reading to the nearest visible graduation for best accuracy.
Binocular Inputs
Magnification
×
Apparent FOV
°
Target height
Target fills 1/3.00 of view — drag the lines to match
Fraction of view filled
/= 0.3333
Fraction exceeds 1 — target is larger than the field of view. Check inputs.
1
True field of view
True FOV = AFOV ÷ Magnification = 65° ÷ 10
→ True FOV = 6.500°
2
Angular size of target
θ = f × True FOV = 0.3333 × 6.500°
→ θ = 2.1667°
3
Convert θ to radians
θrad = θ × (π ÷ 180) = 2.1667° × 0.017453
→ θ_rad = 0.03782
4
Solve for distance
D = H ÷ θrad = 1.500 m ÷ 0.03782
→ D ≈ 39.66 m
Estimated Range
39.7 m
≈ 130 ft / ≈ 43.4 yd
Reusable formula
D = H ÷ [ f × (AFOV ÷ M) × 0.017453 ]
AFOV (apparent field of view) is a spec value printed by the binocular manufacturer. Small-angle approximation used in Step 4; accurate within ~0.1% at typical angles.
Scope Adjustment
Enter the table printed on your ammo box below. Velocity drives the calculated drop; energy is shown
at your target distance for reference. If you also fill in the manufacturer's trajectory column, those
published figures are used directly instead of the estimate — but only while your zero matches the
zero that table was measured at.
Bullet velocity, energy & trajectory table
Range (m)
Velocity (m/s)
Energy (J)
Traj. (mm)
Trajectory is the bullet's path relative to your line of sight: positive is above, negative below,
and 0 marks the zero range. Leave the muzzle row blank.
Scope & zero settings
Adjustment unit
Click value
mil
Total travel (each way)
mil
Zero distance
m
Sight height over bore
cm
Target distance
m
Auto-filled by the "→ Use this range in Ballistics" button on the Scope (MIL) or Binoculars (FOV) tabs.
1
Time of flight (from velocity table)
t(Zero) and t(Target) — integrated from your velocity table, segment by segment
→ t(zero) = 0.000 s · t(target) = 0.000 s
2
Gravity drop at each distance
h = ½ × g × t² (g = 9.807 m/s²)
→ h(zero) = 0.000 m · h(target) = 0.000 m
3
Drop relative to line of sight at target
Drop = (D÷Z)×(hZ+S) − S − hD
→ Drop = 0.000 m
4
Required angular correction
Angle = |Drop| ÷ D → converted to MIL / MOA
→ 0.00 MIL (0.0 MOA)
5
Clicks to dial
Clicks = Angle ÷ Click value
→ 0 clicks
Dial Direction & Clicks
0 clicks UP
≈ 0.00 MIL · 0.0 MOA
At target distance (reference)
Velocity: — · Energy: —
Reusable formula
Drop = (D/Z)(h_Z+S) − S − h_D | Clicks = (|Drop|/D) ÷ click value
Simplified flat-fire model: assumes level ground (no incline/decline), no wind or spin drift, and linear interpolation between your table rows. Velocity/time is derived directly from your box's own printed data rather than a generic ballistic coefficient, which is a reasonable approximation for typical hunting ranges — for competition-grade precision at long range, a full drag-curve solver will be more accurate.
Quick reference — clicks by distance
Recalculates live from the zero, sight height, and bullet table above. The row matching your current zero is highlighted (0 clicks, by definition).
Range
MIL
MOA
Clicks
Compass
Uses your device's orientation sensor to show heading. Requires this app to be hosted on HTTPS and opened on a phone or tablet — it won't work in this in-chat preview. iOS will ask you to confirm the permission.
0°
N
If the heading seems off, calibrate by moving your phone in a slow figure-8. On iPhone this reads true compass heading; on Android it may read magnetic heading depending on the browser.
Level
Uses your device's tilt sensor to check cant and tilt — handy for checking rifle cant or leveling a tripod. Works with the phone lying flat or stood upright. Requires this app to be hosted on HTTPS and opened on a phone or tablet.
Pitch
0.0°
Roll
0.0°
Green stats mean within 1° of level. Lay the phone flat against the rail/rest for the most accurate cant reading.
Experimental — each lens must be calibrated before the range means anything
Camera Rangefinder
Ranges a target from how much of the frame its height fills. Needs camera permission,
and this app served over HTTPS.
Lens
Target height
Frozen
Target fills 30.0% of frame height — drag the lines to match
Estimated Range
—
Calibrate this lens to get a range
Lens calibration
The web platform does not report a camera's focal length or field of view, so it has to be
measured once per lens. Put an object of known height at a known distance, bracket it with the
lines, then calibrate. Stored per lens on this device.
Known height
Known distance (m)
Vertical FOV (°)
Not calibrated.
What this lens reports
Stream & lens properties
—
Zoom is left untouched, since changing it changes the field of view and would invalidate the
calibration. Accuracy depends entirely on how carefully the lines are placed — freeze the frame
before making the final adjustment.
Offline Topo Map · Contours
Pan and zoom to your hunting area, then download it for offline use.
Download this area
Saves every tile in the current view so the map still works with no signal. Downloading needs a
connection; viewing and pinning never do.
Updates are only checked when you press the button.
Display
Compact mode
Hides the step-by-step working and all explanatory text, leaving only the fields you
fill in and the results. Warnings still show.
Scope reticle
How many mils your reticle covers from the centre crosshair out to the edge of the view.
This caps how far the Scope tab can zoom out.
Reticle span ± (mil)
±10 mil · 20 mil total
Scope presets
Turret and zero details for a specific rifle/scope. Applying one fills in the Ballistics tab.
Preset name
Turret unit
Click value
Total travel
Zero (m)
Sight height (cm)
Reticle span ± (mil)
Binocular presets
Magnification and apparent field of view for a pair of binos. Applying one fills in the Binos · FOV tab.
Preset name
Magnification (×)
Apparent FOV (°)
Bullet / load presets
The default velocity and energy table for a load. Applying one fills the Ballistics table.
Values normally come off the ammunition manufacturer's data sheet.
Preset name
Range (m)
Velocity (m/s)
Energy (J)
Traj. (mm)
Storage
Checking…
Presets and pins live in this browser's local storage. Clearing site data in your browser
settings — or uninstalling the app — removes them.