How to create dashed circles with uniform spacing?

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Here is an optimized version of the conic-gradient() solution where you can easily control the number of dashes and the space between

.box {
  --d:4deg; /* distance between dashes */
  --n:30;   /* number of dashes */
  --c:#000; /* color of dashes */
  width: 180px;
  display:inline-block;
  border-radius:50%;
  border:2px solid transparent; /* control the thickness of border*/
  background: 
    linear-gradient(#fff,#fff) padding-box padding-box,
    repeating-conic-gradient(
        var(--c)    0 calc(360deg/var(--n) - var(--d)), 
        transparent 0 calc(360deg/var(--n)) 
    ) border-box;
}

/* keep the element square */
.box:before {
  content:"";
  display:block;
  padding-top:100%;
}
<div class="box"></div>

<div class="box" style="--n:20;border-width:5px;width:150px"></div>

<div class="box" style="--n:8;--d:20deg;border-width:5px;width:150px"></div>

<div class="box" style="--n:10;--d:15deg;border-width:3px;width:100px"></div>

<div class="box" style="--n:10;--d:20deg;border-width:3px;width:100px"></div>

To have full transparency we consider mask

.box {
  --d:4deg; /* distance between dashes */
  --n:30;   /* number of dashes */
  --c:#000; /* color of dashes */
  --b:2px;   /* control the thickness of border*/
  
  width: 180px;
  display:inline-block;
  border-radius:50%;
  background: 
    repeating-conic-gradient(
        var(--c)    0 calc(360deg/var(--n) - var(--d)), 
        transparent 0 calc(360deg/var(--n)));
  -webkit-mask:radial-gradient(farthest-side,transparent calc(100% - var(--b)),#fff calc(100% - var(--b) + 1px));
          mask:radial-gradient(farthest-side,transparent calc(100% - var(--b)),#fff calc(100% - var(--b) + 1px));
}

/* keep the element square */
.box:before {
  content:"";
  display:block;
  padding-top:100%;
}


body {
  background:linear-gradient(to right,yellow,pink);
}
<div class="box"></div>

<div class="box" style="--n:20;--b:5px;width:150px;--c:blue"></div>

<div class="box" style="--n:8;--d:20deg;--b:10px;width:130px;--c:red"></div>

<div class="box" style="--n:18;--d:12deg;--b:8px;width:100px;--c:green"></div>

<div class="box" style="--n:10;--d:20deg;--b:3px;width:100px;--c:purple"></div>

CSS dashed circle with uniform space

To make things funny we can even consider a more complex coloration to the dashes:

.box {
  --d:4deg; /* distance between dashes */
  --n:30;   /* number of dashes */
  --b:2px;   /* control the thickness of border*/
  
  width: 180px;
  display:inline-block;
  border-radius:50%;
  background:linear-gradient(red,blue);
  -webkit-mask:
      radial-gradient(farthest-side,transparent calc(100% - var(--b)),#fff calc(100% - var(--b) + 1px)),
      repeating-conic-gradient(#000 0 calc(360deg/var(--n) - var(--d)),transparent 0 calc(360deg/var(--n)));
  -webkit-mask-composite: source-in;
          mask:
      radial-gradient(farthest-side,transparent calc(100% - var(--b)),#fff calc(100% - var(--b) + 1px)),
      repeating-conic-gradient(#000 0 calc(360deg/var(--n) - var(--d)),transparent 0 calc(360deg/var(--n)));
          mask-composite: intersect;
}

/* keep the element square */
.box:before {
  content:"";
  display:block;
  padding-top:100%;
}


body {
  background:linear-gradient(to right,yellow,pink);
}
<div class="box"></div>

<div class="box" style="--n:20;--b:5px;width:150px;background:conic-gradient(green,orange,black)"></div>

<div class="box" style="--n:8;--d:20deg;--b:10px;width:130px;background:conic-gradient(black,white,black)"></div>

<div class="box" style="--n:18;--d:12deg;--b:8px;width:100px;background:linear-gradient(60deg,red 50%,green 0)"></div>

<div class="box" style="--n:10;--d:20deg;--b:3px;width:100px;background:#fff"></div>

Transparent CSS dashes with conic-gradient and mask

You may for sure want some content inside so better apply the mask/background on a pseudo element to avoid masking the content:

.box {
  --d:4deg; /* distance between dashes */
  --n:30;   /* number of dashes */
  --b:2px;   /* control the thickness of border*/
  
  width: 180px;
  display:inline-flex;
  justify-content:center;
  align-items:center;
  font-size:35px;
  border-radius:50%;
  position:relative;
}
.box::after {
  content:"";
  position:absolute;
  top:0;
  left:0;
  right:0;
  bottom:0;
  z-index:-1;
  border-radius:inherit;
  background:var(--c,linear-gradient(red,blue));
  -webkit-mask:
      radial-gradient(farthest-side,transparent calc(100% - var(--b)),#fff calc(100% - var(--b) + 1px)),
      repeating-conic-gradient(#000 0 calc(360deg/var(--n) - var(--d)),transparent 0 calc(360deg/var(--n)));
  -webkit-mask-composite: source-in;
          mask:
      radial-gradient(farthest-side,transparent calc(100% - var(--b)),#fff calc(100% - var(--b) + 1px)),
      repeating-conic-gradient(#000 0 calc(360deg/var(--n) - var(--d)),transparent 0 calc(360deg/var(--n)));
          mask-composite: intersect;
  
}

/* keep the element square */
.box:before {
  content:"";
  padding-top:100%;
}


body {
  background:linear-gradient(to right,yellow,pink);
}
<div class="box">19</div>

<div class="box" style="--n:20;--b:5px;width:150px;--c:conic-gradient(green,orange,black)">17</div>

<div class="box" style="--n:8;--d:20deg;--b:10px;width:130px;--c:conic-gradient(black,white,black)">5</div>

<div class="box" style="--n:18;--d:12deg;--b:8px;width:100px;--c:linear-gradient(60deg,red 50%,green 0)">9</div>

<div class="box" style="--n:10;--d:20deg;--b:3px;width:100px;--c:#fff">13</div>

Related question to get more CSS ideas to achieve a similar result: CSS Only Pie Chart – How to add spacing/padding between slices?. You will find more supported ways than conic-gradient() (actually it doesn’t work on Firefox) but you are required to use a lot of code unlike the above solution where only one element is needed.

Using SVG you will also need some calculation to make sure you have a uniform spacing:

svg {
  width:200px;
}
<svg viewBox="-3 -3 106 106">
  <!-- 
    The circumference of the circle is 2*PI*R ~ 314.16
    if we want N dashed we use d=314.16/N
    For N = 20 we have d=15.71
    For a gap of 5 we will have "10.71,5" (d - gap,gap)
  -->
  <circle cx="50" cy="50" r="50" 
    stroke-dasharray="10.71, 5" 
    fill="transparent" 
    stroke="black" 
    stroke-width="5" />
</svg>

With CSS variables we can make it easier but it’s not supported in all the browser (actually it doesn’t work in Firefox)

svg {
  --n:20; /* number of dashes*/
  --d:5;  /* distance */
  width:200px;
}

svg circle {
   stroke-dasharray:calc((2*3.14*50)/var(--n) - var(--d)), var(--d); 
}
<svg viewBox="-3 -3 106 106">
  <circle cx="50" cy="50" r="50" fill="transparent" stroke="black" stroke-width="5" />
</svg>

<svg viewBox="-3 -3 106 106" style="width:150px;--n:20;--d:10">
  <circle cx="50" cy="50" r="50" fill="transparent" stroke="red"   stroke-width="5" />
</svg>

<svg viewBox="-3 -3 106 106" style="width:100px;--n:8;--d:15">
  <circle cx="50" cy="50" r="50" fill="transparent" stroke="green" stroke-width="5" />
</svg>

SVG uniform space dashes

We can also easily use the SVG as background to make things more flexible:

.box {
  display:inline-block;
  width:200px;
  background:url('data:image/svg+xml;utf8,<svg xmlns="http://www.w3.org/2000/svg" version="1.1" viewBox="-3 -3 106 106"><circle cx="50" cy="50" r="50" fill="transparent" stroke="black" stroke-width="5" style="stroke-dasharray:29.25, 10" /></svg>') center/contain;
}

.box:before {
  content:"";
  display:block;
  padding-top:100%;
}
<div class="box">

</div>

<div class="box" style="width:150px;">

</div>

<div class="box" style="width:100px;">

</div>

When used as background, you need to manually set the value so you will need a different background each time. We can only make the color easy to change by using the SVG as mask;

.box {
  display:inline-block;
  width:200px;
  position:relative;
}

.box:before {
  content:"";
  display:block;
  padding-top:100%;
}

.box::after {
  content:"";
  position:absolute;
  top:0;
  left:0;
  right:0;
  bottom:0;
  z-index:-1;
  background:var(--c,red);
  -webkit-mask:url('data:image/svg+xml;utf8,<svg xmlns="http://www.w3.org/2000/svg" version="1.1" viewBox="-3 -3 106 106"><circle cx="50" cy="50" r="50" fill="transparent" stroke="black" stroke-width="5" style="stroke-dasharray:29.25, 10" /></svg>') center/contain;
          mask:url('data:image/svg+xml;utf8,<svg xmlns="http://www.w3.org/2000/svg" version="1.1" viewBox="-3 -3 106 106"><circle cx="50" cy="50" r="50" fill="transparent" stroke="black" stroke-width="5" style="stroke-dasharray:29.25, 10" /></svg>') center/contain;
}
<div class="box">

</div>

<div class="box" style="width:150px;--c:linear-gradient(60deg,green 50%,yellow 0);">

</div>

<div class="box" style="width:100px;--c:linear-gradient(red,blue)">

</div>

SVG dashed border with uniform space

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