.w-200-3.block
.w-120-8.block

.block {
  height: 140px;
  width: 100px;
  outline: 1px dashed crimson;
  display: flex;
  align-items: center;
  justify-content: center;
}

.w-200-3 {
  width: 200.3px;
}

.w-120-8 {
  width: 120.8px;
}

const $$ = (sel) => document.querySelectorAll(sel);

const realWidth = (el) => el.getBoundingClientRect().width;

$$(".block").forEach((el) => {
  el.innerText = realWidth(el);
});