Calculate ideal viewing distance such that in-game FOV matches angular size in player's vision

monitor.js

// Calculate ideal viewing distance such that
// in-game FOV matches angular size in player's
// vision.

// 34" 21:9 "ultrawide"
// approx 90-degree horizontal FOV in MSFS
distance({
    h_px: 3440,
    v_px: 1440,
    diagonal_in: 34,
    fov_deg: 90,
});

// 48" 4K monitor
// approx 70-degree horizontal FOV in MSFS
distance({
    h_px: 3840,
    v_px: 2160,
    diagonal_in: 48,
    fov_deg: 70,
});

function round1(val) {
    return Math.round(val * 10) / 10;
}

function round2(val) {
    return Math.round(val * 100) / 100;
}

function distance({h_px, v_px, diagonal_in, fov_deg}) {
    // Derived data...
    let aspect = h_px / v_px;
    let diagonal_px = Math.sqrt(h_px * h_px + v_px * v_px);
    let h_in = diagonal_in * h_px / diagonal_px;
    let v_in = diagonal_in * v_px / diagonal_px;
    let fov_rad = fov_deg * Math.PI / 180;

    // Calc the viewing distance such that
    // half of the FOV (from center to edge) is
    // equal to half the width of the viewing plane
    //
    // Math.tan(fov_rad / 2) * dist == h_in / 2
    //
    let dist = (h_in / 2) / Math.tan(fov_rad / 2);

    console.log(`for ${round1(diagonal_in)} in diagonal with ${round2(aspect)} aspect and ${fov_deg} degree FOV`);
    console.log(`${round1(h_in)} x ${round1(v_in)} inches viewing plane`);
    console.log(`${round1(dist)} inches recommended viewing distance`);
    console.log('');
}

results.txt

for 34 in diagonal with 2.39 aspect and 90 degree FOV
31.4 x 13.1 inches viewing plane
15.7 inches recommended viewing distance

for 48 in diagonal with 1.78 aspect and 70 degree FOV
41.8 x 23.5 inches viewing plane
29.9 inches recommended viewing distance