diff --git a/src/include/units/bits/deduced_unit.h b/src/include/units/bits/deduced_unit.h
index 9f36466b..82a28fc6 100644
--- a/src/include/units/bits/deduced_unit.h
+++ b/src/include/units/bits/deduced_unit.h
@@ -66,6 +66,6 @@ struct derived_ratio<exp_list<E, ERest...>, U, URest...> {
 
 template<DerivedDimension D, Unit... Us>
 using deduced_unit =
-    scaled_unit<typename D::coherent_unit::reference, typename detail::derived_ratio<typename D::recipe, Us...>::ratio>;
+    scaled_unit<typename detail::derived_ratio<typename D::recipe, Us...>::ratio, typename D::coherent_unit::reference>;
 
 }  // namespace units::detail
diff --git a/src/include/units/bits/dimension_op.h b/src/include/units/bits/dimension_op.h
index 6ca7122e..6089dba6 100644
--- a/src/include/units/bits/dimension_op.h
+++ b/src/include/units/bits/dimension_op.h
@@ -71,8 +71,8 @@ inline constexpr bool equivalent_dim = detail::equivalent_dim_impl<D1, D2>::valu
  * @tparam Es zero or more exponents of a derived dimension
  */
 template<Exponent... Es>
-struct unknown_dimension : derived_dimension<unknown_dimension<Es...>, scaled_unit<unknown_unit, ratio<1>>, Es...> {
-  using coherent_unit = scaled_unit<unknown_unit, ratio<1>>;
+struct unknown_dimension : derived_dimension<unknown_dimension<Es...>, scaled_unit<ratio<1>, unknown_unit>, Es...> {
+  using coherent_unit = scaled_unit<ratio<1>, unknown_unit>;
 };
 
 namespace detail {
diff --git a/src/include/units/concepts.h b/src/include/units/concepts.h
index efc1fb51..00801715 100644
--- a/src/include/units/concepts.h
+++ b/src/include/units/concepts.h
@@ -82,7 +82,7 @@ template<typename R>
 concept UnitRatio = Ratio<R> && (R::num * R::den > 0);
 
 // Unit
-template<typename U, UnitRatio R>
+template<UnitRatio R, typename U>
 struct scaled_unit;
 
 template<typename T>
diff --git a/src/include/units/unit.h b/src/include/units/unit.h
index c465c4c8..7ce63081 100644
--- a/src/include/units/unit.h
+++ b/src/include/units/unit.h
@@ -49,14 +49,14 @@ namespace units {
  * @tparam U a unit to use as a reference for this dimension
  * @tparam R a ratio of a reference unit
  */
-template<typename U, UnitRatio R>
-struct scaled_unit : downcast_base<scaled_unit<U, R>> {
-  using reference = U;
+template<UnitRatio R, typename U>
+struct scaled_unit : downcast_base<scaled_unit<R, U>> {
   using ratio = R;
+  using reference = U;
 };
 
 template<Dimension D, UnitRatio R>
-using downcast_unit = downcast<scaled_unit<typename dimension_unit<D>::reference, R>>;
+using downcast_unit = downcast<scaled_unit<R, typename dimension_unit<D>::reference>>;
 
 template<Unit U1, Unit U2>
 struct same_unit_reference : std::is_same<typename U1::reference, typename U2::reference> {};
@@ -70,7 +70,7 @@ struct same_unit_reference : std::is_same<typename U1::reference, typename U2::r
  * @tparam Child inherited class type used by the downcasting facility (CRTP Idiom)
  */
 template<typename Child>
-struct unit : downcast_child<Child, scaled_unit<Child, ratio<1>>> {
+struct unit : downcast_child<Child, scaled_unit<ratio<1>, Child>> {
   static constexpr bool is_named = false;
   using prefix_type = no_prefix;
 };
@@ -95,7 +95,7 @@ struct unknown_unit : unit<unknown_unit> {};
  * @tparam PT no_prefix or a type of prefix family
  */
 template<typename Child, basic_fixed_string Symbol, PrefixType PT>
-struct named_unit : downcast_child<Child, scaled_unit<Child, ratio<1>>> {
+struct named_unit : downcast_child<Child, scaled_unit<ratio<1>, Child>> {
   static constexpr bool is_named = true;
   static constexpr auto symbol = Symbol;
   using prefix_type = PT;
@@ -116,7 +116,7 @@ struct named_unit : downcast_child<Child, scaled_unit<Child, ratio<1>>> {
  * @tparam U a reference unit to scale
  */
 template<typename Child, basic_fixed_string Symbol, PrefixType PT, UnitRatio R, Unit U>
-struct named_scaled_unit : downcast_child<Child, scaled_unit<typename U::reference, ratio_multiply<R, typename U::ratio>>> {
+struct named_scaled_unit : downcast_child<Child, scaled_unit<ratio_multiply<R, typename U::ratio>, typename U::reference>> {
   static constexpr bool is_named = true;
   static constexpr auto symbol = Symbol;
   using prefix_type = PT;
@@ -140,7 +140,7 @@ template<typename Child, Prefix P, Unit U>
 //                                    ratio_multiply<typename P::ratio, typename U::ratio>,
 //                                    typename U::reference> {};
 struct prefixed_unit :
-    downcast_child<Child, scaled_unit<typename U::reference, ratio_multiply<typename P::ratio, typename U::ratio>>> {
+    downcast_child<Child, scaled_unit<ratio_multiply<typename P::ratio, typename U::ratio>, typename U::reference>> {
   static constexpr bool is_named = true;
   static constexpr auto symbol = P::symbol + U::symbol;
   using prefix_type = P::prefix_type;
diff --git a/test/unit_test/runtime/fmt_test.cpp b/test/unit_test/runtime/fmt_test.cpp
index b3123215..c4c3aa03 100644
--- a/test/unit_test/runtime/fmt_test.cpp
+++ b/test/unit_test/runtime/fmt_test.cpp
@@ -110,7 +110,7 @@ TEST_CASE("operator<< on a quantity", "[text][ostream][fmt]")
   {
     SECTION("in terms of base units")
     {
-      const length<scaled_unit<metre, ratio<1'000'000>>> q(123);
+      const length<scaled_unit<ratio<1'000'000>, metre>> q(123);
       stream << q;
 
       SECTION("iostream")
@@ -131,7 +131,7 @@ TEST_CASE("operator<< on a quantity", "[text][ostream][fmt]")
 
     SECTION("in terms of derived units")
     {
-      const energy<scaled_unit<joule, ratio<1, 100>>> q(60);
+      const energy<scaled_unit<ratio<1, 100>, joule>> q(60);
       stream << q;
 
       SECTION("iostream")
diff --git a/test/unit_test/static/quantity_test.cpp b/test/unit_test/static/quantity_test.cpp
index ff4edce3..7dd965f3 100644
--- a/test/unit_test/static/quantity_test.cpp
+++ b/test/unit_test/static/quantity_test.cpp
@@ -112,7 +112,7 @@ using namespace units::si;
 // constexpr quantity<si::dim_length, second, int> error(0);  // should not compile (unit of a different dimension)
 // constexpr quantity<si::dim_length, metre, quantity<si::dim_length, metre, int>> error(0);  // should not compile (quantity used as Rep)
 // constexpr quantity<metre, si::dim_length, double> error(0);  // should not compile (reordered arguments)
-// constexpr quantity<si::dim_length, scaled_unit<metre, ratio<-1, 1>>, int> error(0);  // should not compile (negative unit ratio)
+// constexpr quantity<si::dim_length, scaled_unit<ratio<-1, 1>, metre>, int> error(0);  // should not compile (negative unit ratio)
 
 // member types
 
@@ -236,23 +236,23 @@ static_assert(std::is_same_v<decltype(1.0 * length<metre, int>()), length<metre,
 static_assert(
     std::is_same_v<decltype(velocity<metre_per_second, int>() * si::time<second, int>()), length<metre, int>>);
 static_assert(
-    std::is_same_v<decltype(velocity<metre_per_second, int>() * si::time<hour, int>()), length<scaled_unit<metre, ratio<3600>>, int>>);
+    std::is_same_v<decltype(velocity<metre_per_second, int>() * si::time<hour, int>()), length<scaled_unit<ratio<3600>, metre>, int>>);
 static_assert(std::is_same_v<decltype(length<metre>() * si::time<minute>()),
-                             quantity<unknown_dimension<units::exp<dim_length, 1>, units::exp<dim_time, 1>>, scaled_unit<unknown_unit, ratio<60>>>>);
+                             quantity<unknown_dimension<units::exp<dim_length, 1>, units::exp<dim_time, 1>>, scaled_unit<ratio<60>, unknown_unit>>>);
 static_assert(std::is_same_v<decltype(1 / si::time<second, int>()), frequency<hertz, int>>);
-static_assert(std::is_same_v<decltype(1 / si::time<minute, int>()), frequency<scaled_unit<hertz, ratio<1, 60>>, int>>);
+static_assert(std::is_same_v<decltype(1 / si::time<minute, int>()), frequency<scaled_unit<ratio<1, 60>, hertz>, int>>);
 static_assert(std::is_same_v<decltype(1 / frequency<hertz, int>()), si::time<second, int>>);
 static_assert(std::is_same_v<decltype(1 / length<kilometre>()),
-                             quantity<unknown_dimension<units::exp<dim_length, -1>>, scaled_unit<unknown_unit, ratio<1, 1000>>>>);
+                             quantity<unknown_dimension<units::exp<dim_length, -1>>, scaled_unit<ratio<1, 1000>, unknown_unit>>>);
 static_assert(std::is_same_v<decltype(length<metre, int>() / 1.0), length<metre, double>>);
 static_assert(std::is_same_v<decltype(length<metre, int>() / length<metre, double>()), double>);
 static_assert(std::is_same_v<decltype(length<kilometre, int>() / length<metre, double>()), double>);
 static_assert(
     std::is_same_v<decltype(length<metre, int>() / si::time<second, int>()), velocity<metre_per_second, int>>);
 static_assert(
-    std::is_same_v<decltype(length<metre>() / si::time<minute>()), velocity<scaled_unit<metre_per_second, ratio<1, 60>>>>);
+    std::is_same_v<decltype(length<metre>() / si::time<minute>()), velocity<scaled_unit<ratio<1, 60>, metre_per_second>>>);
 static_assert(std::is_same_v<decltype(si::time<minute>() / length<metre>()),
-                             quantity<unknown_dimension<units::exp<dim_length, -1>, units::exp<dim_time, 1>>, scaled_unit<unknown_unit, ratio<60>>>>);
+                             quantity<unknown_dimension<units::exp<dim_length, -1>, units::exp<dim_time, 1>>, scaled_unit<ratio<60>, unknown_unit>>>);
 static_assert(std::is_same_v<decltype(length<metre, int>() % short(1)), length<metre, int>>);
 static_assert(std::is_same_v<decltype(length<metre, int>() % length<metre, short>(1)), length<metre, int>>);
 
@@ -316,7 +316,7 @@ static_assert(std::is_same_v<common_quantity<length<kilometre, long long>, lengt
 
 // quantity_cast
 
-static_assert(std::is_same_v<decltype(quantity_cast<scaled_unit<metre, ratio<1>>>(2km))::unit, metre>);
+static_assert(std::is_same_v<decltype(quantity_cast<scaled_unit<ratio<1>, metre>>(2km))::unit, metre>);
 
 static_assert(quantity_cast<length<metre, int>>(2km).count() == 2000);
 static_assert(quantity_cast<length<kilometre, int>>(2000m).count() == 2);
diff --git a/test/unit_test/static/si_test.cpp b/test/unit_test/static/si_test.cpp
index 1fec088e..19a3cb8e 100644
--- a/test/unit_test/static/si_test.cpp
+++ b/test/unit_test/static/si_test.cpp
@@ -191,7 +191,7 @@ static_assert(10V * 1F == 10C);
 
 // velocity
 
-static_assert(std::is_same_v<decltype(1km / 1s), velocity<scaled_unit<metre_per_second, ratio<1000>>, std::int64_t>>);
+static_assert(std::is_same_v<decltype(1km / 1s), velocity<scaled_unit<ratio<1000>, metre_per_second>, std::int64_t>>);
 
 static_assert(10m / 5s == 2mps);
 static_assert(10 / 5s * 1m == 2mps);
diff --git a/test/unit_test/static/unit_test.cpp b/test/unit_test/static/unit_test.cpp
index 84dc5e10..f7b7aa42 100644
--- a/test/unit_test/static/unit_test.cpp
+++ b/test/unit_test/static/unit_test.cpp
@@ -45,11 +45,11 @@ struct metre_per_second : unit<metre_per_second> {};
 struct dim_velocity : derived_dimension<dim_velocity, metre_per_second, exp<dim_length, 1>, exp<dim_time, -1>> {};
 struct kilometre_per_hour : deduced_unit<kilometre_per_hour, dim_velocity, kilometre, hour> {};
 
-static_assert(std::is_same_v<downcast<scaled_unit<metre, ratio<1>>>, metre>);
-static_assert(std::is_same_v<downcast<scaled_unit<metre, ratio<1, 100>>>, centimetre>);
-static_assert(std::is_same_v<downcast<scaled_unit<metre, ratio<yard::ratio::num, yard::ratio::den>>>, yard>);
-static_assert(std::is_same_v<downcast<scaled_unit<metre, ratio_multiply<typename yard::ratio, ratio<1, 3>>>>, foot>);
-static_assert(std::is_same_v<downcast<scaled_unit<metre_per_second, ratio_divide<typename kilometre::ratio, typename hour::ratio>>>, kilometre_per_hour>);
+static_assert(std::is_same_v<downcast<scaled_unit<ratio<1>, metre>>, metre>);
+static_assert(std::is_same_v<downcast<scaled_unit<ratio<1, 100>, metre>>, centimetre>);
+static_assert(std::is_same_v<downcast<scaled_unit<ratio<yard::ratio::num, yard::ratio::den>, metre>>, yard>);
+static_assert(std::is_same_v<downcast<scaled_unit<ratio_multiply<typename yard::ratio, ratio<1, 3>>, metre>>, foot>);
+static_assert(std::is_same_v<downcast<scaled_unit<ratio_divide<typename kilometre::ratio, typename hour::ratio>, metre_per_second>>, kilometre_per_hour>);
 
 static_assert(centimetre::symbol == "cm");
 static_assert(kilometre::symbol == "km");