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Scope Field of View & Width Calculator

Convert true angular field to width at a chosen distance, or estimate it from apparent field using an explicit convention. Compare metres, feet and yards.

Use this result well

Inputs that matter
Angle input, True field (degrees), Apparent field (degrees), Magnification, and 3 more
Output to expect
Scope Field of View & Width
  • Check the units and required inputs before comparing results.
  • Keep the assumptions with a copied result so you can reproduce the calculation later.
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Reference & details

How it works

Convert true angle to linear width

For full true angular field θ and viewing distance d, field width is 2d tan(θ/2). Angles entered in degrees are converted to radians for trigonometry. The width lies across a plane perpendicular to the viewing axis, not along a curved landscape.

Source: Nikon: Real field and field width

Choose the apparent-field convention deliberately

The traditional ratio uses true field = apparent field / magnification. The half-angle tangent convention instead gives true field = 2 atan(tan(apparent field/2) / magnification). Nikon documents both conventions. Select the one used by your source; an unknown convention cannot yield a defensible inferred angle. These conversions do not model lens distortion.

Source: Nikon: Apparent-field calculation conventions

Normalize the reference distance

Distance may be entered in metres or international yards. One international yard is exactly 0.9144 m and one international foot is 0.3048 m. Results include widths in all three units. A field quoted at 1000 yards must not be compared directly with one quoted at 1000 metres.

Source: NIST SI unit conversion factors

Keep uncertainty and practical limits visible

Use the angle for the actual eyepiece and magnification setting. Rounded specifications carry uncertainty, and apparent-field inference adds a convention assumption. This tool does not determine useful edge sharpness, recognize birds or decide how much habitat has been surveyed.

Updated: September 2026

Example Scenarios

Convert known angular fields to widths at the same distance before comparing instruments.

Calculate the width for a subject plane at your entered distance rather than retaining a fixed 1000-yard reference.

Compare the two apparent-field conventions only as an assumptions exercise when evaluating how source definitions affect the result.

Common Mistakes to Avoid

Treating apparent and true angular fields as interchangeable

Use the Angle input selector and the corresponding input. Apparent-field mode also requires magnification and a known convention.

Mixing yards and metres

Select the unit that belongs to the distance. The tool converts using international yards and feet.

Calling an inferred field a measured field

Retain the angle basis shown in the result and verify against the instrument documentation.

FAQ

Approximately 47.888813 m or 157.115529 ft across the perpendicular subject plane. The calculation uses the tangent formula rather than a rounded feet-per-degree multiplier.

Dividing the full apparent angle by magnification is different from applying the half-angle tangent relation. For 60° apparent field at 20×, they imply 3° and about 3.307055° respectively.

Use a published or measured true angular field if available. Apparent-field mode deliberately waits for a convention choice instead of guessing.

No. It calculates geometric width from the supplied angle and distance. Actual edge quality, terrain and detection conditions are separate.

About Scope Field of View & Width Calculator

Use a published or measured true angular field when available, then enter the viewing distance. If only an apparent-field specification is available, choose its documented calculation convention. The result describes a flat subject plane and does not measure your scope.