diff --git a/_column-setter.scss b/_column-setter.scss
index 2e8d2e9..086cc81 100644
--- a/_column-setter.scss
+++ b/_column-setter.scss
@@ -32,22 +32,22 @@
 @function wrong-type($type, $arg2:null, $arg3:null) {
 	@if $arg2
 	and $arg3 {
-		@return "'#{$arg2}' and '#{$arg3}' are not #{$type}s"
+		@return "'#{$arg2}' and '#{$arg3}' are not #{$type}s";
 	}
 	@if not $arg3 {
-		@return "'#{$arg2}' is not a #{$type}"
+		@return "'#{$arg2}' is not a #{$type}";
 	}
 }
 @function missing($number) {
 	@if $number < 2 {
-		@return "an argument is missing. "
+		@return "an argument is missing. ";
 	}
 	@if $number >= 2 {
-		@return "arguments are missing. "
+		@return "arguments are missing. ";
 	}
 }
 @function optional($number,$current,$correct) {
-	@return "the optional #{$number} argument (currently '#{$current}') will only accept a value of '#{$correct}'. "
+	@return "the optional #{$number} argument (currently '#{$current}') will only accept a value of '#{$correct}'. ";
 }
 
 // ----------------------------------------
@@ -67,7 +67,7 @@
 // 40em
 
 @function bp-attribute($bp-name, $bp-attribute) {
-	@return map-get(map-get($breakpoints, $bp-name), $bp-attribute)
+	@return map-get(map-get($breakpoints, $bp-name), $bp-attribute);
 }
 
 // ----------------------------------------
@@ -78,16 +78,16 @@
 
 @function bp-validator() {
 	@if type-of($mar) != number or unitless($mar) == false {
-		@warn "Here is the bp-validator $mar warning."
+		@warn "Here is the bp-validator $mar warning.";
 	}
 	@if type-of($col) != number or unitless($col) == false {
-		@warn "Here is the bp-validator $col warning."
+		@warn "Here is the bp-validator $col warning.";
 	}
 	@if type-of($gut) != number or unitless($gut) == false {
-		@warn "Here is the bp-validator $gut warning."
+		@warn "Here is the bp-validator $gut warning.";
 	}
 	@if type-of($pad) != number or unitless($pad) == false {
-		@warn "Here is the bp-validator $pad warning."
+		@warn "Here is the bp-validator $pad warning.";
 	}
 	@for $i from 1 through length($breakpoints) {
 		@if type-of(map-get(map-get($breakpoints, (nth(map-keys($breakpoints), $i))), cols)) != number or unitless(map-get(map-get($breakpoints, (nth(map-keys($breakpoints), $i))), cols)) == false {
@@ -112,8 +112,8 @@
 //
 // 538
 
-@function width($width) {
-	@return (($col * $width) + ($gut * ($width - 1)))
+@function fluidWidth($width) {
+	@return (($col * $width) + ($gut * ($width - 1)));
 }
 
 // ----------------------------------------
@@ -134,60 +134,160 @@
 
 $colspan-lesson: "A 'colspan' function call must include the unitless numeric column widths of both the target and its container, e.g. 'colspan(4,8)'. The target width can also be specified as 'p' (for $pad width) or 'g' (for $gut width).";
 
-@function colspan($target:null,$container:null) {
-	@if $target
-	and $container {
-		@if $target == "m"
-		and (type-of($container) == "number" and unitless($container) == true) {
-			@return percentage($mar / (width($container) + ($mar * 2)))
-		}
-		@if $target == "p"
-		and (type-of($container) == "number" and unitless($container) == true) {
-			@return percentage($pad / width($container))
-		}
-		@if $target == "g"
-		and (type-of($container) == "number" and unitless($container) == true) {
-			@return percentage($gut / width($container))
-		}
-		@if (type-of($target) != "number" or unitless($target) == false)
-		and (type-of($container) != "number" or unitless($container) == false)
-		and $target != "m"
-		and $target != "p"
-		and $target != "g" {
-			@warn invalid("colspan",$target,$container) + wrong-type("unitless number",$target,$container) + ". " + $colspan-lesson;
-			@return false;
-		}
-		@if (type-of($target) != "number" or unitless($target) == false)
-		and (type-of($container) == "number" and unitless($container) == true) {
-			@warn invalid("colspan",$target,$container) + wrong-type("unitless number",$target) + ". " + $colspan-lesson;
-			@return false;
-		}
-		@if ((type-of($target) == "number" and unitless($target) == true) and (type-of($container) != "number" or unitless($container) == false))
-		or ($target == "m" and (type-of($container) != "number" or unitless($container) == false))
-		or ($target == "p" and (type-of($container) != "number" or unitless($container) == false))
-		or ($target == "g" and (type-of($container) != "number" or unitless($container) == false)) {
-			@warn invalid("colspan",$target,$container) + wrong-type("unitless number",$container) + ". " + $colspan-lesson;
-			@return false;
-		}
-	}
-	@if $target
-	and not $container {
-		@if (type-of($target) == "number" and unitless($target) == true) {
-			@warn invalid(colspan,$target) + missing(1) + $colspan-lesson;
-			@return false;
-		} @else {
-			@warn invalid(colspan,$target) + wrong-type("unitless number",$target) + ", and " + missing(1) + $colspan-lesson;
+@function colspan($target:null, $container:null, $addgut:false, $neg:false) {
+	@if $target and $container { // If a target and container have been specified
+		@if $target == $container { // If the target and container are the same
+			@return 100%;
+		} @else if type-of($container) == "number" and unitless($container) == true { // If the container is a unitless number
+
+			$fluidMar: true;
+			$fluidCol: true;
+			$fluidGut: true;
+			$fluidPad: true;
+			$addgutAmount: 0;
+			$negAmount: 1;
+			$negOpen: "";
+			$negClose: "";
+
+			@if unitless($mar) == false { // If margins are fixed width
+				$fluidMar: false;
+			}
+			@if unitless($col) == false { // If columns are fixed width
+				$fluidCol: false;
+			}
+			@if unitless($gut) == false { // If gutters are fixed width
+				$fluidGut: false;
+				@if $addgut == true { // If a gutter is added to the desired width
+					$addgutAmount: $gut;
+				}
+			} @else if $addgut == true { // If gutters are fluid width and a gutter is added to the desired width
+				@if $fluidCol == true { // If columns are fluid width
+					$addgutAmount: percentage($gut / fluidWidth($container));
+				} @else { // If columns are fixed width
+					$addgutAmount: 1;
+				}
+			}
+			@if unitless($pad) == false { // If padding is fixed width
+				$fluidPad: false;
+			}
+			@if $neg == true { // If the desired width is negative
+				$negAmount: -1;
+				$negOpen: "(";
+				$negClose: ") * " + $negAmount;
+			}
+
+			@if $target == "p" { // If the target is "p" (padding)
+				@if $addgut == true { // If a gutter is added to the desired width
+					@warn "$addgut can't be used with p or g.";
+					@return false;
+				} @else if $fluidPad == false { // If padding is fixed width
+					@return $pad * $negAmount;
+				} @else if $fluidCol == true and $fluidGut == true { // If padding, columns, and gutters are fluid width
+					@return percentage($pad / fluidWidth($container)) * $negAmount;
+				} @else if $fluidCol == true { // If padding and columns are fluid width and gutters are fixed width
+					@return calc(#{$negOpen}((100% - #{$gut * ($container - 1)}) / #{$container}) * #{$pad / $col}#{$negClose});
+				} @else if $fluidGut == true { // If padding and gutters are fluid width and columns are fixed width
+					@return calc(#{$negOpen}((100% - #{$col * $container}) / #{$container - 1}) * #{$pad / $gut}#{$negClose});
+				} @else { // If padding is fluid width and columns and gutters are fixed width
+					@warn "For padding to be fluid width, columns and/or gutters must also be fluid width.";
+					@return false;
+				}
+			} @else if $target == "g" { // If the target is "g" (gutter)
+				@if $addgut == true { // If a gutter is added to the desired width
+					@warn "$addgut can't be used with p or g.";
+					@return false;
+				} @else if $fluidGut == false { // If gutters are fixed width
+					@return $gut * $negAmount;
+				} @else if $fluidCol == true { // If gutters and columns are fluid width
+					@return (percentage($gut / fluidWidth($container)) + $addgutAmount) * $negAmount;
+				} @else { // If gutters are fluid width and columns are fixed width
+					@return calc(#{$negOpen}(100% - #{$col * $container}) / #{$container - 1}#{$negClose});
+				}
+			} @else if type-of($target) == "number" and unitless($target) == true { // If the target is a unitless number
+				@if $fluidCol == false { // If columns are fixed width
+					@if $fluidGut == true { // If gutters are fluid width
+						@return calc(#{$negOpen}(((100% - #{$col * $container}) / #{$container - 1}) * #{$target - 1 + $addgutAmount}) + #{$col * $target}#{$negClose});
+					} @else if unit($col) == unit($gut) { // If columns and gutters are fixed width and use the same units
+						@return (($col * $target) + ($gut * ($target - 1)) + $addgutAmount) * $negAmount;
+					} @else { // If columns and gutters are fixed width and use different units
+						@return calc(#{$negOpen}#{($col * $target)} + #{($gut * ($target - 1)) + $addgutAmount}#{$negClose});
+					}
+				} @else if $fluidGut == true { // If columns are fluid width and gutters are fluid width
+					@return (percentage(fluidWidth($target) / fluidWidth($container)) + $addgutAmount) * $negAmount;
+				} @else { // If columns are fluid width and gutters are fixed width
+					@return calc(#{$negOpen}(((100% - #{$gut * ($container - 1)}) / #{$container}) * #{$target}) + #{($gut * ($target - 1)) + $addgutAmount}#{$negClose});
+				}
+			} @else { // If the specified target is not "m", "p", "g", or a unitless number
+				@warn "A colspan() target must be either 'p' (padding), 'g' (gutter), or a unitless number.";
+				@return false;
+			}
+		} @else { // If the specified container is not a unitless number
+			@warn "A colspan() container must be a unitless number.";
 			@return false;
 		}
-	}
-	@if not $target {
-		@warn invalid(colspan) + missing(2) + $colspan-lesson;
+	} @else if $target and not $container { // If a target is specified but not a container
+		@warn "colspan() requires a container to be specified.";
+		@return false;
+	} @else if not $target { // If neither target nor container are specified
+		@warn "colspan() requires a target and container to be specified.";
 		@return false;
-	} @else {
-		@return percentage(width($target) / width($container))
 	}
 }
 
+// @function colspan($target:null,$container:null) {
+// 	@if $target
+// 	and $container {
+// 		@if $target == "m"
+// 		and (type-of($container) == "number" and unitless($container) == true) {
+// 			@return percentage($mar / (width($container) + ($mar * 2)));
+// 		}
+// 		@if $target == "p"
+// 		and (type-of($container) == "number" and unitless($container) == true) {
+// 			@return percentage($pad / width($container));
+// 		}
+// 		@if $target == "g"
+// 		and (type-of($container) == "number" and unitless($container) == true) {
+// 			@return percentage($gut / width($container));
+// 		}
+// 		@if (type-of($target) != "number" or unitless($target) == false)
+// 		and (type-of($container) != "number" or unitless($container) == false)
+// 		and $target != "m"
+// 		and $target != "p"
+// 		and $target != "g" {
+// 			@warn invalid("colspan",$target,$container) + wrong-type("unitless number",$target,$container) + ". " + $colspan-lesson;
+// 			@return false;
+// 		}
+// 		@if (type-of($target) != "number" or unitless($target) == false)
+// 		and (type-of($container) == "number" and unitless($container) == true) {
+// 			@warn invalid("colspan",$target,$container) + wrong-type("unitless number",$target) + ". " + $colspan-lesson;
+// 			@return false;
+// 		}
+// 		@if ((type-of($target) == "number" and unitless($target) == true) and (type-of($container) != "number" or unitless($container) == false))
+// 		or ($target == "m" and (type-of($container) != "number" or unitless($container) == false))
+// 		or ($target == "p" and (type-of($container) != "number" or unitless($container) == false))
+// 		or ($target == "g" and (type-of($container) != "number" or unitless($container) == false)) {
+// 			@warn invalid("colspan",$target,$container) + wrong-type("unitless number",$container) + ". " + $colspan-lesson;
+// 			@return false;
+// 		}
+// 	}
+// 	@if $target
+// 	and not $container {
+// 		@if (type-of($target) == "number" and unitless($target) == true) {
+// 			@warn invalid(colspan,$target) + missing(1) + $colspan-lesson;
+// 			@return false;
+// 		} @else {
+// 			@warn invalid(colspan,$target) + wrong-type("unitless number",$target) + ", and " + missing(1) + $colspan-lesson;
+// 			@return false;
+// 		}
+// 	}
+// 	@if not $target {
+// 		@warn invalid(colspan) + missing(2) + $colspan-lesson;
+// 		@return false;
+// 	} @else {
+// 		@return percentage(width($target) / width($container));
+// 	}
+// }
+
 // ------------------------------------------------------------
 // MIXINS
 // ------------------------------------------------------------
@@ -356,7 +456,7 @@ $grid-lesson: "A 'grid' mixin call must include a valid class name, e.g. 'grid(c
 			@each $bp, $value in $breakpoints {
 				@include breakpoint-min($bp) {
 					@if map-has-key(map-get($breakpoints, $bp), margin) {
-						margin: 0 colspan(bp-attribute($bp, margin), width(bp-attribute($bp, cols)) + (bp-attribute($bp, margin) * 2));
+						margin: 0 colspan(bp-attribute($bp, margin), fluidWidth(bp-attribute($bp, cols)) + (bp-attribute($bp, margin) * 2));
 					} @else {
 						margin: 0 colspan(m, bp-attribute($bp, cols));
 					}
@@ -371,11 +471,11 @@ $grid-lesson: "A 'grid' mixin call must include a valid class name, e.g. 'grid(c
 				max-width: $max-width;
 				$bp-final: nth(map-keys($breakpoints), -1); // Name of the widest breakpoint
 				@if map-has-key(map-get($breakpoints, $bp-final), margin) {
-					@media screen and (min-width: ((((bp-attribute($bp-final, margin) / width(bp-attribute($bp-final, cols))) * $max-width) * 2) + $max-width)) {
+					@media screen and (min-width: ((((bp-attribute($bp-final, margin) / fluidWidth(bp-attribute($bp-final, cols))) * $max-width) * 2) + $max-width)) {
 						margin: 0 auto;
 					}
 				} @else {
-					@media screen and (min-width: (((($mar / width(bp-attribute($bp-final, cols))) * $max-width) * 2) + $max-width)) {
+					@media screen and (min-width: (((($mar / fluidWidth(bp-attribute($bp-final, cols))) * $max-width) * 2) + $max-width)) {
 						margin: 0 auto;
 					}
 				}