diff --git a/src/include/units/physical/si/time.h b/src/include/units/physical/si/time.h
index 9bd60783..fcca48db 100644
--- a/src/include/units/physical/si/time.h
+++ b/src/include/units/physical/si/time.h
@@ -33,7 +33,8 @@ struct nanosecond : prefixed_unit<nanosecond, nano, second> {};
 struct microsecond : prefixed_unit<microsecond, micro, second> {};
 struct millisecond : prefixed_unit<millisecond, milli, second> {};
 struct minute : named_scaled_unit<minute, "min", no_prefix, ratio<60>, second> {};
-struct hour : named_scaled_unit<hour, "h", no_prefix, ratio<3600>, second> {};
+struct hour : named_scaled_unit<hour, "h", no_prefix, ratio<60>, minute> {};
+struct day : named_scaled_unit<hour, "d", no_prefix, ratio<24>, hour> {};
 
 struct dim_time : physical::dim_time<second> {};
 
@@ -66,6 +67,10 @@ constexpr auto operator""min(long double l) { return time<minute, long double>(l
 constexpr auto operator""h(unsigned long long l) { return time<hour, std::int64_t>(l); }
 constexpr auto operator""h(long double l) { return time<hour, long double>(l); }
 
+// d
+constexpr auto operator""_d(unsigned long long l) { return time<day, std::int64_t>(l); }
+constexpr auto operator""_d(long double l) { return time<day, long double>(l); }
+
 }  // namespace literals
 
 }  // namespace units::si
diff --git a/test/unit_test/static/si_test.cpp b/test/unit_test/static/si_test.cpp
index 724064ab..de326a95 100644
--- a/test/unit_test/static/si_test.cpp
+++ b/test/unit_test/static/si_test.cpp
@@ -75,7 +75,10 @@ static_assert(1us == 1000ns);
 static_assert(1ms == 1000us);
 static_assert(1s == 1000ms);
 static_assert(1min == 60s);
+static_assert(1h == 60min);
 static_assert(1h == 3600s);
+static_assert(1_d == 24h);
+static_assert(1_d == 86'400s);
 
 static_assert(nanosecond::symbol == "ns");
 static_assert(microsecond::symbol == "µs");