What Is FOV, and Why Are There Three Kinds?
Field of view (FOV) describes the angular span of a camera view. Horizontal FOV spans the left and right edges, vertical FOV spans top to bottom, and diagonal FOV spans opposite corners. Their numbers differ even when they describe exactly the same virtual perspective, because the screen or render viewport has a width-to-height ratio.
Games do not all expose the same type of FOV setting. Some report horizontal FOV for the current screen, some report vertical FOV, and some describe horizontal FOV at a 4:3 reference aspect before converting it for modern displays. You must know the game's actual convention to convert correctly. This tool does not detect games or read their settings.
How to Use This Calculator
- Enter your game's FOV value (from 0.01° to 179.99°). Select horizontal, vertical, diagonal, or horizontal at 4:3 baseline only if you know the game's convention.
- Enter your current screen or render aspect width and height. You can type a ratio such as 16 and 9, enter the corresponding resolution such as 1920 and 1080, or use the preset buttons. The ratio matters, not the pixel count. Marketing labels such as “21:9” can be approximate; use the exact game render resolution when known.
- Read the calculated horizontal, vertical, and diagonal FOV for the current aspect. The wedge drawings illustrate horizontal and vertical angular spread; they do not simulate a game image.
- Optionally set a target aspect ratio (such as 21:9). Choose whether to keep vertical FOV constant (Hor+), horizontal FOV constant, or diagonal FOV constant. Compare the target angles to the originals.
- Use 4:3 Baseline Example to learn about that convention, or Reset All to restore the default. Copy Summary or Download JSON to save your calculated values. Confirm your own game's FOV behavior before using any result as a settings recommendation.
How the Calculation Works
For a centered, rectilinear perspective camera, let the viewport aspect ratio be a = width ÷ height. The relationship between half-angles is based on trigonometry, not a simple multiplication of FOV degrees:
vFOV = 2 × atan(tan(hFOV ÷ 2) ÷ a)
hFOV = 2 × atan(tan(vFOV ÷ 2) × a)
For diagonal FOV, tan(dFOV ÷ 2) = √[tan²(hFOV ÷ 2) + tan²(vFOV ÷ 2)]. These equations operate in radians internally, with degree conversions for displayed results. At a 4:3 horizontal baseline, the entered horizontal FOV is first converted to its equivalent vertical FOV at 4:3, then translated to the current aspect.
At a new aspect ratio, Hor+ keeps vertical FOV constant and recomputes horizontal FOV; keeping horizontal FOV fixed does the reverse. Keeping diagonal FOV constant preserves the diagonal half-angle tangent while redistributing its horizontal and vertical components.
Understanding Your Result
The three angles always describe the same calculated view at the current aspect. For example, with a normal horizontal FOV of 90° at 16:9, the equivalent vertical FOV is approximately 58.72° and the diagonal FOV about 97.85°. A setting of 90° horizontal at a 4:3 baseline instead corresponds to about 106.26° horizontal on a 16:9 screen when the vertical perspective is held constant.
| Conversion model | When changing to a wider aspect ratio |
|---|---|
| Keep vertical (Hor+) | Vertical angle remains equal; horizontal FOV widens. |
| Keep horizontal | Horizontal angle remains equal; vertical FOV becomes narrower. |
| Keep diagonal | Diagonal angle remains equal; the other two angles change. |
These are mathematical choices. Real games may use a fixed baseline aspect, letterbox, crop, zoom or stretch the rendered image, and may change FOV while aiming down sights (ADS).
Benefits and Practical Uses
- Compare horizontal and vertical settings when games label their FOV differently.
- See what a 4:3 horizontal reference value would mean on a 16:9 or ultrawide viewport.
- Model how changing from a standard monitor to an ultrawide might affect view angles under different FOV policies.
- Export the calculated camera geometry for later comparison with game documentation or testing.
Common Mistakes to Avoid
- Treating all “90 FOV” values as identical: the axis and possible baseline matter as much as the degree value.
- Multiplying degrees by an aspect-ratio factor: FOV conversion requires tangent and arctangent.
- Confusing game camera FOV with physical monitor viewing angle: the latter also depends on screen size and viewing distance.
- Assuming every game is Hor+: aspect handling can depend on the game, engine, mode, version and ADS zoom.
- Entering stretched display output instead of render viewport: use the game's actual camera/render aspect, which may differ from the monitor's native ratio.
Frequently Asked Questions
Does a wider FOV make me a worse or better player?
Neither inherently - a wider FOV gives more peripheral awareness at the cost of making distant targets appear smaller, while a narrower FOV does the opposite. Most players settle on whichever feels natural and doesn't cause discomfort.
Why does my FOV look different after changing my aspect ratio?
Because horizontal and vertical FOV are linked through the aspect ratio - changing your resolution's ratio while keeping the same reported FOV value will visibly change how much you can see on the wider or taller axis.
What FOV do most competitive players use?
It varies by game and genre, but many competitive FPS players on a standard 16:9 monitor land somewhere between 90 and 103 horizontal FOV, largely as a personal comfort preference.
Why Field of View Conversions Aren't a Simple Ratio
Because projected image edges subtend angles, the camera's horizontal and vertical view widths are proportional to the tangents of their half-angles, not the angles themselves. As an example, a 90° horizontal 4:3 view becomes about 106.26° horizontal at 16:9 if the vertical angle stays the same; directly multiplying 90° by (16:9)/(4:3) would incorrectly give 120°. At extreme FOV settings, nonlinear behavior becomes even more significant.
These conversions assume rectilinear projection, a symmetric view frustum and no special zoom, fish-eye or off-axis projection. Virtual reality headsets and certain games can use other projection geometry.
Conclusion
Correct FOV conversions make it easier to understand settings and compare camera behavior between screen ratios. Check which axis and baseline your game reports, then use this calculator to translate the resulting angles. If you need help identifying a viewport ratio, visit the Aspect Ratio Calculator.