FPS cap / LFC dead-band calculator for VRR panels (free, web)
Posted: 27 Sep 2026, 06:27
I made a small web calculator for the numbers I kept working out by hand on my VRR monitor: where to put the fps cap, whether LFC has a valid multiplier for my 1% low, and how much motion blur a given frame rate gives in pixels.
The cap part runs two rules side by side. One is G-SYNC 101's minus 3 fps. The other is a fixed frametime margin of 1/3600 s, which is the Reflex formula RealNC posted here in June (Hz * 3600 / (Hz + 3600)), so with Reflex selected it gives 138 at 144 Hz and 225 at 240 Hz. The two rules drift apart as refresh goes up: at 540 Hz, minus 3 fps leaves 0.010 ms of margin, while the frametime rule caps at 470.
For LFC it lists the frame-rate ranges with no valid multiple. A 48-60 Hz window has three: 30-48, 20-24 and 15-16 fps. That is the idealised model, since the driver decides when LFC actually kicks in, as RealNC has pointed out.
It doesn't measure input lag and doesn't recommend hardware.
FPS cap and LFC calculator
Disclosure: I built and run the site. English isn't my first language and this post was written with AI help. If any of the numbers are wrong, tell me here and I'll fix the calculator.
The cap part runs two rules side by side. One is G-SYNC 101's minus 3 fps. The other is a fixed frametime margin of 1/3600 s, which is the Reflex formula RealNC posted here in June (Hz * 3600 / (Hz + 3600)), so with Reflex selected it gives 138 at 144 Hz and 225 at 240 Hz. The two rules drift apart as refresh goes up: at 540 Hz, minus 3 fps leaves 0.010 ms of margin, while the frametime rule caps at 470.
For LFC it lists the frame-rate ranges with no valid multiple. A 48-60 Hz window has three: 30-48, 20-24 and 15-16 fps. That is the idealised model, since the driver decides when LFC actually kicks in, as RealNC has pointed out.
It doesn't measure input lag and doesn't recommend hardware.
FPS cap and LFC calculator
Disclosure: I built and run the site. English isn't my first language and this post was written with AI help. If any of the numbers are wrong, tell me here and I'll fix the calculator.