Generated by SassMeister.com.

SassMeister-input.scss

// ----
// Sass (v3.4.14)
// Compass (v1.0.3)
// ----

$row-width: 1800px;
$row-height: 420px;

$my-sass-map: (
    1: 600px,
    2: 430px,
    3: 340px,
    4: 430px
);

@function sum($args...) {
  $sum: 0;
  
  @each $arg in $args {
    $sum: $sum + $arg;
  }
  
  @return $sum;
}

// Any function that you know of that would be able to add all values in all keys together.
// Ultimately I'd be checking the total sum against another variable.

@each $key, $value in $my-sass-map {
    .row1-#{$key} {
        // here I would have an if statement that would check the total value
        // of $my-sass-maps against $row-width
        @if sum(map-keys($my-sass-map)...) == $row-width {
          width: ($value / $row-width) * 100%;
        } @else {
          @warn "Please check total widths of $my-sass-maps"
        }
    }

    .row1-#{$key}-inner {
        padding-bottom: ($row-height/$value) * 100%;
    }
}

SassMeister-output.css

.row1-1-inner {
  padding-bottom: 70%;
}

.row1-2-inner {
  padding-bottom: 97.67442%;
}

.row1-3-inner {
  padding-bottom: 123.52941%;
}

.row1-4-inner {
  padding-bottom: 97.67442%;
}