Estimate how far away something is by entering its real size (or your height above water/ground) and how many mils or MOA it measures in your binocular or scope reticle.
Advanced options
How to use our Binoculars Range Calculator
- Pick a Method: choose "Size-based ranging" if you know the target height/width, or "Horizon method" if you measured down from the horizon.
- Choose your Reticle unit: Mil (mrad) or MOA, matching your optic.
- Enter the Measured angle in reticle (how many mils or MOA the target spans, or how many mils/MOA down from the horizon). It must be greater than 0.
- If you chose Size-based ranging, enter the Target size and pick the Target size unit (height or width, just be consistent with what you measured in the reticle).
- If you chose Horizon method, open Advanced options and enter your Height above water/ground and its Height unit.
- (Optional) Open Advanced options and choose an Output distance unit so the result matches your map, notes, or range card.
- (Optional) If your optic is SFP and you know the calibration magnification, turn on Apply SFP magnification correction and enter the magnifications.
- Click Calculate. If you see a note about a very small angle, re-check your reticle reading because tiny angle errors can cause big distance errors.
Definitions
Range (distance): How far you are from the target, along the line of sight.
Reticle: The marked scale (lines/dots) you look through to measure how big something appears.
Mil (mrad): A milliradian, an angle unit used by many reticles. The classic "mil relation" uses 1000 in the formula.
MOA: Minute of angle, another angle unit used by some scopes.
Angular size: The amount of reticle units (mils or MOA) the target covers, or the amount you measure down from the horizon.
Horizon method: A ranging method that uses your height above the water/ground and the mils down from the horizon to the target [1].
SFP magnification correction: A fix for Second Focal Plane optics where the reticle scale is only correct at one magnification.
Methodology
What the calculator is doing
This calculator converts a real-world size (or your height above the surface) and a reticle angle into an estimated distance using standard reticle ranging relationships used with reticular binoculars [1] and common field procedures [2].
Step 1: Choose the angle used in the math (with optional SFP correction)
effective_angle = measured_angle * (calibration_magnification / measured_magnification)
If SFP magnification correction is off, then effective_angle equals your measured_angle. If it is on, both magnifications must be greater than 0 to avoid divide-by-zero.
Step 2A: Size-based ranging (known target size)
If Reticle unit is Mil (mrad), the calculator uses the mil relation in metric form after converting your Target size unit into meters.
distance_m = target_size_m * 1000 / effective_mils
If Reticle unit is MOA, the calculator first converts the target size into inches, then computes distance in yards using the common 95.5 constant, and finally converts to your selected output unit.
distance_yd = (target_size_in * 95.5) / effective_moa
Step 2B: Horizon method (known height above water/ground)
In Horizon method, the calculator converts Height above water/ground into meters and uses the same mil relation structure commonly shown for reticle binocular ranging from the horizon [1].
distance_m = height_above_surface_m * 1000 / effective_mils_down
Unit conversions and outputs
The calculator computes an internal base distance (meters or yards, depending on the formula) and then converts to your chosen Output distance unit. It also shows a secondary readout in a couple of common units to help you sanity-check.
Validation and edge cases
If the measured angle is blank, not a number, or less than or equal to 0, the calculator stops and shows an error asking you to enter an angle greater than 0. In Size-based ranging, target size must be greater than 0. In Horizon method, height above water/ground must be greater than 0. If SFP correction is on, both magnifications must be greater than 0. If a calculation produces a non-finite value (NaN or Infinity), the distance is shown as N/A with an error explaining what to fix. If the angle is very small, the calculator shows a warning that small angle reading errors can create large distance errors.