diff --git a/src/systems/si/include/units/si/constants.h b/src/systems/si/include/units/si/constants.h
index 0239f46c..b8fe0eb2 100644
--- a/src/systems/si/include/units/si/constants.h
+++ b/src/systems/si/include/units/si/constants.h
@@ -62,8 +62,11 @@ inline constexpr auto avogadro_constant = (1 / isq::amount_of_substance)[avogadr
 // clang-format off
 inline constexpr struct standard_gravity_unit :
   constant_unit<"g", mag<ratio{980'665, 100'000}> * metre / square<second>> {} standard_gravity_unit;
+inline constexpr struct magnetic_constant_unit :
+  constant_unit<basic_symbol_text{"μ₀", "u0"}, mag<4> * mag_pi * mag_power<10, -7> * henry / metre> {} magnetic_constant_unit;
 // clang-format on
 
 inline constexpr auto standard_gravity = isq::acceleration[standard_gravity_unit];
+inline constexpr auto magnetic_constant = isq::magnetic_constant[magnetic_constant_unit];
 
 }  // namespace units::si