標準差

html,
body,
svg {
  height: 100%;
}

<svg viewBox="0 0 480 200" xmlns="http://www.w3.org/2000/svg">
  <filter id="gaussianBlur1">
    <feGaussianBlur stdDeviation="1" />
  </filter>
  <filter id="gaussianBlur2">
    <feGaussianBlur stdDeviation="5" />
  </filter>
  <filter id="gaussianBlur3" x="-30%" y="-30%" width="160%" height="160%">
    <feGaussianBlur stdDeviation="10" />
  </filter>

  <circle cx="100" cy="100" r="50" style="filter: url(#gaussianBlur1);" />
  <circle
    cx="100"
    cy="100"
    r="50"
    style="filter: url(#gaussianBlur2); transform: translateX(140px);" />
  <circle
    cx="100"
    cy="100"
    r="50"
    style="filter: url(#gaussianBlur3); transform: translateX(280px);" />
</svg>