The name
lerp(a, b, t) = a + (b − a) × t
t is the fraction of the way from a to b. For scroll smoothing, every frame moves a fraction of the remaining distance, so the motion eases out.
95% caught up in 474 ms
28 frames at 60 Hz. A fixed factor runs faster when the screen does.
Frame-rate independent a = 1 − exp(−dt / τ)
τ = 158 ms · dt = 16.7 ms. Use that form when the rate should not change the feel.
Drag inside the page, or press Scroll. It eases with the factor and rate above.
A page
The wheel sets a target.
Each frame closes part of the gap. What remains shrinks, so the motion eases out.
Still catching up.
A smaller factor leaves more distance for the next frame. A larger one arrives sooner, and can feel abrupt.
Arrived.
70 sites are known for a measured smooth scroll, from 0.056 to 0.693. Median of these leads: 0.1.
Each number is the smooth-scroll factor already in that site's public lead. Many great sites use native scroll, no lerp. The library measures intros, hovers and transitions too.
See smooth scroll as a technique