Important disclaimer

The information and results produced by this website are for informational purposes only. They are based on the formulas and assumptions described in this tool and are not medical, legal, or professional advice. We make no warranties, express or implied, about accuracy or fitness for a particular purpose.

If the underlying equations or their application are incomplete, outdated, or incorrect, the outputs shown here will also be wrong. Do not rely on this site as a substitute for qualified professional judgment, clinical testing, or legal review. We are not liable for any decisions, losses, or other consequences arising from use of this calculator. By continuing, you acknowledge and accept these limitations.

Visual Acuity Calculator

Calculate equivalent Snellen visual acuity.

About This Tool

This calculator determines equivalent Snellen visual acuity from an object's physical size and its distance from the viewer. It also categorizes the viewing distance (Near, Intermediate, Far) and reports the expected accommodative demand.

Clinical Logic & Formulas (For Professionals)

Visual Angle: Uses the exact geometric split-triangle formula to determine the subtended angle in arc-minutes:

2 × arctan(size / (2 × distance)) × (10800 / π)

Equivalent Acuity: Derives the Snellen denominator based on the standard 5 arc-minute letter:

(visual_angle_minutes / 5) × 20

Accommodative Demand: Calculated in Diopters based on viewing distance:

1 / distance_in_meters

Alternate acuity (N = 20, D = Snellen denominator): MAR = D / N; LogMAR = log10(MAR); decimal = N / D; metric 6/X uses Dmetric = D × (6/20), shown as 6/round(Dmetric); M-units at the entered distance: M = distance_m × (D / N).

Object Size Specifications
Viewing Distance Specifications