diff --git a/macros/ui/niceTables.pl b/macros/ui/niceTables.pl
index 665003861..bca5e26ce 100644
--- a/macros/ui/niceTables.pl
+++ b/macros/ui/niceTables.pl
@@ -88,8 +88,9 @@ =head3 All output formats
 
 C<r> for right-aligned column
 
-C<p{width}> for a column with left-aligned paragraphs of fixed width.
-The width needs to be absolute to work in all output formats.
+C<p{width}> for a column with left-aligned paragraphs of the given width.
+The width can be an absolute width or (unlike in LaTeX) a positive decimal number at most 1.
+If it is a decimal, it will be interpreted as a portion of the available width.
 
 C<X> for a column that expands to fill (see C<Xratio> below),
 and will have left-aligned paragraphs 
@@ -536,7 +537,8 @@ sub TableEnvironment {
 	if ($main::displayMode eq 'TeX') {
 		my $tabulartype  = $hasX ? 'tabularx'                        : 'tabular';
 		my $tabularwidth = $hasX ? "$tableOpts->{Xratio}\\linewidth" : '';
-		$rows = latexEnvironment($rows, $tabulartype, [ $tabularwidth, '[t]', $tableOpts->{texalignment} ], ' ');
+		my $texalignment = $tableOpts->{texalignment} =~ s/p\{0*(0(\.\d*)?|1(\.0*)?)\}/p\{$1\\linewidth\}/gr;
+		$rows = latexEnvironment($rows, $tabulartype, [ $tabularwidth, '[t]', $texalignment ], ' ');
 		$rows = prefix($rows, '\centering%') if $tableOpts->{center};
 		$rows = prefix($rows, '\renewcommand{\arraystretch}{' . ($tableOpts->{padding}[0] + 1) . '}', '');
 		$rows = prefix($rows, '\setlength{\tabcolsep}{' . ($tableOpts->{padding}[1] * 10) . 'pt}',    '');
@@ -566,7 +568,6 @@ sub TableEnvironment {
 			$ptxmargins = "${leftmargin}% ${rightmargin}%";
 			$ptxwidth .= '%';
 		} elsif (!$tableOpts->{center}) {
-			$ptxwidth   = '100%';
 			$ptxmargins = '0% 0%';
 		}
 		if ($tableOpts->{LaYoUt}) {
@@ -574,8 +575,8 @@ sub TableEnvironment {
 				$rows,
 				'sbsgroup',
 				{
-					width   => $ptxwidth,
 					margins => $ptxmargins,
+					widths  => $cols
 				}
 			);
 		} elsif (!$tableOpts->{LaYoUt}) {
@@ -584,13 +585,12 @@ sub TableEnvironment {
 				$rows,
 				'tabular',
 				{
-					valign     => ($tableOpts->{valign} ne 'middle') ? $tableOpts->{valign} : '',
-					bottom     => $tableOpts->{horizontalrules}      ? 'minor'              : '',
-					rowheaders => $tableOpts->{rowheaders}           ? 'yes'                : '',
-					margins    => $ptxmargins,
-					width      => $ptxwidth,
-					left       => $ptxleft,
-					top        => $ptxtop,
+					valign        => ($tableOpts->{valign} ne 'middle') ? $tableOpts->{valign} : '',
+					bottom        => $tableOpts->{horizontalrules}      ? 'minor'              : '',
+					'row-headers' => $tableOpts->{rowheaders}           ? 'yes'                : '',
+					width         => $ptxwidth,
+					left          => $ptxleft,
+					top           => $ptxtop,
 				}
 			);
 		}
@@ -674,30 +674,34 @@ sub Cols {
 		}
 
 		if ($main::displayMode eq 'PTX') {
-			my $ptxhalign = '';
-			$ptxhalign = 'center' if ($align->{halign} eq 'c');
-			$ptxhalign = 'right'  if ($align->{halign} eq 'r');
-			my $ptxright = '';
-			$ptxright = getPTXthickness($align->{right});
-			my $ptxtop = '';
-			$ptxtop = getPTXthickness($top);
-			my $ptxwidth = '';
-			$ptxwidth = getWidthPercent($align->{width}) if $align->{width};
-			$ptxwidth = ($tableOpts->{Xratio} / $#$alignment * 100) . '%'
-				if ($align->{halign} eq 'X');
-			$ptxwidth = getWidthPercent($width) if $width;
-			push(
-				@cols,
-				tag(
-					'', 'col',
-					{
-						halign => $ptxhalign,
-						right  => $ptxright,
-						top    => $ptxtop,
-						width  => $ptxwidth
-					}
-				)
-			);
+			if ($tableOpts->{LaYoUt}) {
+				push @cols, ($align->{width} ? getWidthPercent($align->{width}) : '%');
+			} else {
+				my $ptxhalign = '';
+				$ptxhalign = 'center' if ($align->{halign} eq 'c');
+				$ptxhalign = 'right'  if ($align->{halign} eq 'r');
+				my $ptxright = '';
+				$ptxright = getPTXthickness($align->{right});
+				my $ptxtop = '';
+				$ptxtop = getPTXthickness($top);
+				my $ptxwidth = '';
+				$ptxwidth = getWidthPercent($align->{width}) if $align->{width};
+				$ptxwidth = ($tableOpts->{Xratio} / $#$alignment * 100) . '%'
+					if ($align->{halign} eq 'X');
+				$ptxwidth = getWidthPercent($width) if $width;
+				push(
+					@cols,
+					tag(
+						'', 'col',
+						{
+							halign => $ptxhalign,
+							right  => $ptxright,
+							top    => $ptxtop,
+							width  => $ptxwidth
+						}
+					)
+				);
+			}
 		} else {
 			my $htmlright = '';
 			$htmlright .= css('border-right', 'solid 2px')
@@ -705,6 +709,12 @@ sub Cols {
 			$htmlright .= css('border-right', getRuleCSS($align->{right}));
 			my $htmltop = '';
 			$htmltop .= css('border-top', getRuleCSS($top));
+			my $htmlwidth = '';
+			if ($align->{width}) {
+				$htmlwidth = css('width', $align->{width});
+				$htmlwidth = css('width', getWidthPercent($align->{width}))
+					if ($align->{width} =~ /^0*(0(\.\d*)?|1(\.0*)?)$/);
+			}
 
 			# $i starts at 1, but columncss indexing starts at 0
 			my $htmlcolcss = css($columnscss->[ $i - 1 ]);
@@ -712,11 +722,39 @@ sub Cols {
 				$htmlcolcss .= css('background-color', ($1 ? '#' : '') . $2);
 			}
 
-			push(@cols, tag('', 'col', { style => "${htmlright}${htmltop}${htmlcolcss}" }));
+			push(@cols, tag('', 'col', { style => "${htmlright}${htmltop}${htmlcolcss}${htmlwidth}" }));
 		}
 
 	}
 
+	if ($main::displayMode eq 'PTX' && $tableOpts->{LaYoUt}) {
+		my @decimalcols = map { substr $_, 0, -1 } @cols;
+		my $total       = 0;
+		my $count       = 0;
+		for (@decimalcols) {
+			if ($_ eq '') {
+				$count++;
+			} else {
+				$total += $_;
+			}
+		}
+		# determine if somewhere in the alignment there are X columns
+		my $hasX = 0;
+		for my $align (@$alignment) {
+			if ($align->{halign} eq 'X') {
+				$hasX = 1;
+				last;
+			}
+		}
+		my $width = ($hasX ? $tableOpts->{Xratio} * 100 : 100);
+		my $fill  = ($count != 0) ? int(($width - $total) / $count * 10**4) / 10**4 : 0;
+		for (@decimalcols) {
+			$_ = $fill if ($_ eq '');
+		}
+		@cols = map { $_ . '%' } @decimalcols;
+		return join(' ', @cols);
+	}
+
 	return join("\n", @cols);
 
 }
@@ -805,52 +843,11 @@ sub Rows {
 				if (!$ptxleft && $rowArray->[0]{halign} && $alignment->[0]{left});
 
 			if ($tableOpts->{LaYoUt}) {
-				my $ptxwidthsum = 0;
-				my $ptxautocols = $#alignment;
-				for my $j (1 .. $#alignment) {
-					if ($rowArray->[ $j - 1 ]{width}) {
-						$ptxwidthsum +=
-							substr getWidthPercent($tableArray->[ $j - 1 ]{width}),
-							0, -1;
-						$ptxautocols -= 1;
-					} elsif ($alignment->[$j]{width}) {
-						$ptxwidthsum += substr getWidthPercent($alignment->[$j]{width}), 0, -1;
-						$ptxautocols -= 1;
-					}
-				}
-
-				# determine if somewhere in the overall alignment, there are X columns
-				my $hasX = 0;
-				for my $align (@$alignment) {
-					if ($align->{halign} eq 'X') {
-						$hasX = 1;
-						last;
-					}
-				}
-				my $leftoverspace =
-					(($hasX) ? $tableOpts->{Xratio} * 100 : 100) - $ptxwidthsum;
-				my $divvyuptherest = 0;
-				$divvyuptherest = int($leftoverspace / $ptxautocols * 10000) / 10000
-					unless ($ptxautocols == 0);
-				my @ptxwidths;
-				for my $j (1 .. $#alignment) {
-					if ($rowOpts->[ $j - 1 ]{width}) {
-						push(@ptxwidths, getWidthPercent($rowOpts->[ $j - 1 ]{width}));
-					} elsif ($alignment->[$j]{width}) {
-						push(@ptxwidths, getWidthPercent($alignment->[$j]{width}));
-					} else {
-						push(@ptxwidths, $divvyuptherest . '%');
-					}
-				}
-
-				my $ptxwidths = join(" ", @ptxwidths);
 				$row = tag(
 					$row,
 					'sidebyside',
 					{
-						valign  => ($valign) ? $valign : $tableOpts->{valign},
-						margins => '0% 0%',
-						widths  => $ptxwidths,
+						valign => ($valign) ? $valign : $tableOpts->{valign},
 					}
 				);
 			} else {
@@ -954,6 +951,7 @@ sub Row {
 				|| ($tableOpts->{rowheaders} && $tableOpts->{headerrules} && $i == 0))
 			{
 				my $columntype = $cellOpts->{halign};
+				$columntype = $columntype =~ s/p\{0*(0(\.\d*)?|1(\.0*)?)\}/p\{$1\\linewidth\}/gr;
 				$columntype = $cellAlign->{halign} // 'l' unless $columntype;
 				$columntype = 'p{' . $tableOpts->{Xratio} / ($#$rowArray + 1) . "\\linewidth}"
 					if ($columntype eq 'X');
@@ -1038,8 +1036,11 @@ sub Row {
 				if ($cellAlign->{halign} eq 'c');
 			$css .= css('text-align', 'right')
 				if ($cellAlign->{halign} eq 'r');
-			$css .= css('width', $cellAlign->{width})
-				if ($cellAlign->{width});
+			if ($cellAlign->{width} =~ /^0*(0(\.\d*)?|1(\.0*)?)$/) {
+				$css .= css('width', getWidthPercent($1));
+			} elsif ($cellAlign->{width}) {
+				$css .= css('width', $cellAlign->{width});
+			}
 			$css .= css('font-weight', 'bold')
 				if ($cellAlign->{tex} =~ /\\bfseries/);
 			$css .= css('font-style', 'italic')
@@ -1075,8 +1076,11 @@ sub Row {
 				if ($cellOpts->{halign} =~ /^c/);
 			$css .= css('text-align', 'right') if ($cellOpts->{halign} =~ /^r/);
 			$css .= css('text-align', 'left')  if ($cellOpts->{halign} =~ /^p/);
-			$css .= css('width',      $1)
-				if ($cellOpts->{halign} =~ /^p\{([^}]*?)}/);
+			if ($cellOpts->{halign} =~ /^p\{0*(0(\.\d*)?|1(\.0*)?)}/) {
+				$css .= css('width', getWidthPercent($1));
+			} elsif ($cellOpts->{halign} =~ /^p\{([^}]*?)}/) {
+				$css .= css('width', $1);
+			}
 			$css .= css('font-weight', 'bold')
 				if ($cellOpts->{tex} =~ /\\bfseries/);
 			$css .= css('font-style', 'italic')
@@ -1581,29 +1585,39 @@ sub getPTXthickness {
 }
 
 sub getWidthPercent {
-	my $absWidth = shift;
-	my $x        = 0;
-	my $unit     = 'cm';
-	if ($absWidth =~ /^(\.\d+|\d+\.?\d*)\s*(\w+)/) {
+	my $width = shift;
+	return $width             if (substr($width, -1) eq '%');
+	return $width * 100 . '%' if ($width =~ /^0*(0(\.\d*)?|1(\.0*)?)$/);
+	my $x    = 0;
+	my $unit = 'cm';
+	if ($width =~ /^(\.\d+|\d+\.?\d*)\s*(\w+)$/) {
 		$x    = $1;
 		$unit = $2;
 	}
-	my %convert_to_cm = (
-		'pt' => 1 / 864 * 249 / 250 * 12 * 2.54,
-		'mm' => 1 / 10,
-		'cm' => 1,
-		'in' => 2.54,
-		'ex' => 0.15132,
-		'em' => 0.35146,
-		'mu' => 0.35146 / 8,
-		'sp' => 1 / 864 * 249 / 250 * 12 * 2.54 / 65536,
-		'bp' => 2.54 / 72,
-		'dd' => 1 / 864 * 249 / 250 * 12 * 2.54 * 1238 / 1157,
-		'pc' => 1 / 864 * 249 / 250 * 12 * 2.54 * 12,
-		'cc' => 1 / 864 * 249 / 250 * 12 * 2.54 * 1238 / 1157 * 12,
-		'px' => 2.54 / 72,
+	my %convert_to_pt = (
+		# units with related absolute defintions
+		# the following are as TeX defines them
+		pt => 1,
+		pc => 12,
+		in => 72.27,
+		mm => 72.27 / 25.4,
+		cm => 72.27 / 2.54,
+		sp => 1 / 65536,
+		dd => 1238 / 1157,
+		cc => 12 * 1238 / 1157,
+		bp => 72.27 / 72,
+		# CSS defines 1 px to be 1/96 of an inch
+		# note that px is not a legal unit in TeX
+		px => 72 / 96,
+		# units relative to font
+		# the following are based on TeX default font
+		# (10pt Computer Modern)
+		em => 10.00002,
+		ex => 4.30554,
 	);
-	return (int($x * $convert_to_cm{$unit} / (6.25 * 2.54) * 10000) / 100) . '%';
+	# This is only used for PTX output, and a PTX document's default width is 340pt.
+	# We offer a percent with up to six significant digits
+	return (int($x * $convert_to_pt{$unit} / 340 * 10**6) / 10**4) . '%';
 }
 
 sub hrule {