diff --git a/src/include/units/bits/common_quantity.h b/src/include/units/bits/common_quantity.h
index 33cf6970..ceabedf6 100644
--- a/src/include/units/bits/common_quantity.h
+++ b/src/include/units/bits/common_quantity.h
@@ -52,7 +52,11 @@ struct common_quantity_impl<quantity<D1, U1, Rep1>, quantity<D2, U2, Rep2>, Rep>
 template<typename D1, typename U1, typename Rep1, typename D2, typename U2, typename Rep2, typename Rep>
 struct common_quantity_impl<quantity<D1, U1, Rep1>, quantity<D2, U2, Rep2>, Rep> {
   using dimension = conditional<is_instantiation_of<D1, unknown_dimension>, D2, D1>;
-  using type = quantity<dimension, downcast_unit<dimension, common_ratio(U1::ratio, U2::ratio)>, Rep>;
+  static constexpr ratio r1 = D1::base_units_ratio * U1::ratio;
+  static constexpr ratio r2 = D2::base_units_ratio * U2::ratio;
+  static constexpr ratio cr = common_ratio(r1, r2);
+  using unit = downcast_unit<dimension, cr / dimension::base_units_ratio>;
+  using type = quantity<dimension, unit, Rep>;
 };
 
 template<typename D, typename U, typename Rep>
diff --git a/src/include/units/quantity_cast.h b/src/include/units/quantity_cast.h
index 965f1159..d1a093f6 100644
--- a/src/include/units/quantity_cast.h
+++ b/src/include/units/quantity_cast.h
@@ -313,7 +313,14 @@ struct quantity_cast_impl<To, CRatio, CRep, false, true, false> {
 template<typename Q1, typename Q2>
 constexpr ratio cast_ratio(const Q1& from, const Q2& to)
 {
-  return quantity_ratio(from) / quantity_ratio(to);
+  using FromU = Q1::unit;
+  using ToU = Q2::unit;
+  if constexpr(same_unit_reference<FromU, ToU>::value) {
+    return FromU::ratio / ToU::ratio;
+  }
+  else {
+    return quantity_ratio(from) / quantity_ratio(to);
+  }
 }
 
 }  // namespace detail
diff --git a/test/unit_test/static/si_fps_test.cpp b/test/unit_test/static/si_fps_test.cpp
index b857400f..0bca26fc 100644
--- a/test/unit_test/static/si_fps_test.cpp
+++ b/test/unit_test/static/si_fps_test.cpp
@@ -69,8 +69,7 @@ static_assert(fps::length<fps::foot>(1) == 0.3048q_m);
 static_assert(fps::mass<fps::pound>(1) == 0.45359237q_kg);
 static_assert(fps::time<fps::second>(1) == 1q_s);
 static_assert(fps::speed<fps::foot_per_second>(1) == 0.3048q_m_per_s);
-static_assert(fps::area<fps::square_foot>(1) > 0.09290303q_m2 &&
-              fps::area<fps::square_foot>(1) < 0.09290305q_m2);
+static_assert(fps::area<fps::square_foot>(1) == 0.09290304q_m2);
 static_assert(fps::acceleration<fps::foot_per_second_sq>(1) == 0.3048q_m_per_s2);
 static_assert(fps::force<fps::poundal>(1) > 0.138254q_N && 
               fps::force<fps::poundal>(1) < 0.138256q_N);
@@ -113,8 +112,7 @@ static_assert(1q_ft == 0.3048q_m);
 static_assert(1q_lb == 0.45359237q_kg);
 static_assert(1q_s  == 1q_s);
 static_assert(1q_ft_per_s == 0.3048q_m_per_s);
-static_assert(1q_ft2 > 0.09290303q_m2 &&
-              1q_ft2 < 0.09290305q_m2);
+static_assert(1q_ft2 == 0.09290304q_m2);
 static_assert(1q_ft_per_s2 == 0.3048q_m_per_s2);
 static_assert(1q_pdl > 0.138254q_N && 
               1q_pdl < 0.138256q_N);