--- a/dom/svg/DOMSVGLength.cpp
+++ b/dom/svg/DOMSVGLength.cpp
@@ -208,20 +208,22 @@ float DOMSVGLength::GetValue(ErrorResult
   }
   if (HasOwner()) {
     float value = InternalItem().GetValueInUserUnits(Element(), Axis());
     if (!IsFinite(value)) {
       aRv.Throw(NS_ERROR_FAILURE);
     }
     return value;
   }
-  if (mUnit == SVGLength_Binding::SVG_LENGTHTYPE_NUMBER ||
-      mUnit == SVGLength_Binding::SVG_LENGTHTYPE_PX) {
-    return mValue;
+
+  float unitToPx;
+  if (UserSpaceMetrics::ResolveAbsoluteUnit(mUnit, unitToPx)) {
+    return mValue * unitToPx;
   }
+
   // else [SVGWG issue] Can't convert this length's value to user units
   // ReportToConsole
   aRv.Throw(NS_ERROR_FAILURE);
   return 0.0f;
 }
 
 void DOMSVGLength::SetValue(float aUserUnitValue, ErrorResult& aRv) {
   if (mIsAnimValItem) {

--- a/dom/svg/SVGAnimatedLength.cpp
+++ b/dom/svg/SVGAnimatedLength.cpp
@@ -199,32 +199,50 @@ float SVGAnimatedLength::GetPixelsPerUni
         SVGElementMetrics(static_cast<SVGElement*>(content)), aUnitType);
   }
   return GetPixelsPerUnit(NonSVGFrameUserSpaceMetrics(aFrame), aUnitType);
 }
 
 // See https://www.w3.org/TR/css-values-3/#absolute-lengths
 static const float DPI = 96.0f;
 
-float SVGAnimatedLength::GetPixelsPerUnit(const UserSpaceMetrics& aMetrics,
-                                          uint8_t aUnitType) const {
+bool UserSpaceMetrics::ResolveAbsoluteUnit(uint8_t aUnitType, float& aRes) {
   switch (aUnitType) {
     case SVGLength_Binding::SVG_LENGTHTYPE_NUMBER:
     case SVGLength_Binding::SVG_LENGTHTYPE_PX:
-      return 1;
+      aRes = 1;
+      break;
     case SVGLength_Binding::SVG_LENGTHTYPE_MM:
-      return DPI / MM_PER_INCH_FLOAT;
+      aRes = DPI / MM_PER_INCH_FLOAT;
+      break;
     case SVGLength_Binding::SVG_LENGTHTYPE_CM:
-      return 10.0f * DPI / MM_PER_INCH_FLOAT;
+      aRes = 10.0f * DPI / MM_PER_INCH_FLOAT;
+      break;
     case SVGLength_Binding::SVG_LENGTHTYPE_IN:
-      return DPI;
+      aRes = DPI;
+      break;
     case SVGLength_Binding::SVG_LENGTHTYPE_PT:
-      return DPI / POINTS_PER_INCH_FLOAT;
+      aRes = DPI / POINTS_PER_INCH_FLOAT;
+      break;
     case SVGLength_Binding::SVG_LENGTHTYPE_PC:
-      return 12.0f * DPI / POINTS_PER_INCH_FLOAT;
+      aRes = 12.0f * DPI / POINTS_PER_INCH_FLOAT;
+      break;
+    default:
+      return false;
+  }
+  return true;
+}
+
+float SVGAnimatedLength::GetPixelsPerUnit(const UserSpaceMetrics& aMetrics,
+                                          uint8_t aUnitType) const {
+  float res;
+  if (UserSpaceMetrics::ResolveAbsoluteUnit(aUnitType, res)) {
+    return res;
+  }
+  switch (aUnitType) {
     case SVGLength_Binding::SVG_LENGTHTYPE_PERCENTAGE:
       return aMetrics.GetAxisLength(mCtxType) / 100.0f;
     case SVGLength_Binding::SVG_LENGTHTYPE_EMS:
       return aMetrics.GetEmLength();
     case SVGLength_Binding::SVG_LENGTHTYPE_EXS:
       return aMetrics.GetExLength();
     default:
       MOZ_ASSERT_UNREACHABLE("Unknown unit type");

--- a/dom/svg/SVGAnimatedLength.h
+++ b/dom/svg/SVGAnimatedLength.h
@@ -28,16 +28,17 @@ class SMILValue;
 namespace dom {
 class DOMSVGAnimatedLength;
 class DOMSVGLength;
 class SVGAnimationElement;
 class SVGViewportElement;
 
 class UserSpaceMetrics {
  public:
+  static bool ResolveAbsoluteUnit(uint8_t aUnitType, float& aRes);
   virtual ~UserSpaceMetrics() = default;
 
   virtual float GetEmLength() const = 0;
   virtual float GetExLength() const = 0;
   virtual float GetAxisLength(uint8_t aCtxType) const = 0;
 };
 
 class UserSpaceMetricsWithSize : public UserSpaceMetrics {

--- a/testing/web-platform/meta/svg/types/scripted/SVGLength-px.html.ini
+++ b/testing/web-platform/meta/svg/types/scripted/SVGLength-px.html.ini
@@ -2,24 +2,8 @@
   [SVGLength, converting from 'px' to other units (detached), percentage]
     expected: FAIL
 
   [SVGLength, converting from 'px' to other units (detached), ems]
     expected: FAIL
 
   [SVGLength, converting from 'px' to other units (detached), exs]
     expected: FAIL
-
-  [SVGLength, converting from 'px' to other units (detached), cm]
-    expected: FAIL
-
-  [SVGLength, converting from 'px' to other units (detached), mm]
-    expected: FAIL
-
-  [SVGLength, converting from 'px' to other units (detached), in]
-    expected: FAIL
-
-  [SVGLength, converting from 'px' to other units (detached), pt]
-    expected: FAIL
-
-  [SVGLength, converting from 'px' to other units (detached), pc]
-    expected: FAIL
-

--- a/testing/web-platform/tests/svg/types/scripted/SVGLength-px.html
+++ b/testing/web-platform/tests/svg/types/scripted/SVGLength-px.html
@@ -67,17 +67,17 @@ test(function() {
 
 test(function() {
   var length = svgElement.createSVGLength();
   length.valueAsString = "48px";
   length.convertToSpecifiedUnits(SVGLength.SVG_LENGTHTYPE_CM);
   var referenceValue = 48 * 2.54 / cssPixelsPerInch;
   assert_equals(length.valueAsString, referenceValue.toFixed(2) + "cm");
   assert_approx_equals(length.valueInSpecifiedUnits, referenceValue, 0.01);
-  assert_equals(length.value, 48);
+  assert_approx_equals(length.value, 48, 0.001);
   assert_equals(length.unitType, SVGLength.SVG_LENGTHTYPE_CM);
 }, document.title + ", cm");
 
 test(function() {
   var length = svgElement.createSVGLength();
   length.valueAsString = "48px";
   length.convertToSpecifiedUnits(SVGLength.SVG_LENGTHTYPE_MM);
   var referenceValue = 48 * 25.4 / cssPixelsPerInch;
@@ -114,9 +114,9 @@ test(function() {
   length.valueAsString = "16px";
   length.convertToSpecifiedUnits(SVGLength.SVG_LENGTHTYPE_PC);
   var referenceValue = 16 / cssPixelsPerInch * 6;
   // Don't check valueAsString here, it's unreliable across browsers.
   assert_equals(length.valueInSpecifiedUnits, referenceValue);
   assert_equals(length.value, 16);
   assert_equals(length.unitType, SVGLength.SVG_LENGTHTYPE_PC);
 }, document.title + ", pc");
-</script>
\ No newline at end of file
+</script>