diff --git a/examples/webgl_materials_envmaps_parallax.html b/examples/webgl_materials_envmaps_parallax.html
index a58a351b765871e3d07c67039f4efe98313ae1d7..ae382d367fd75b3b68803f6ce31e7bf8b6519602 100644
--- a/examples/webgl_materials_envmaps_parallax.html
+++ b/examples/webgl_materials_envmaps_parallax.html
@@ -175,9 +175,7 @@
 
 					#elif defined( ENVMAP_TYPE_EQUIREC )
 
-						vec2 sampleUV;
-						sampleUV.y = asin( clamp( reflectVec.y, - 1.0, 1.0 ) ) * RECIPROCAL_PI + 0.5;
-						sampleUV.x = atan( reflectVec.z, reflectVec.x ) * RECIPROCAL_PI2 + 0.5;
+						vec2 sampleUV = equirectUv( reflectVec );
 
 						#ifdef TEXTURE_LOD_EXT
 
diff --git a/src/extras/PMREMGenerator.js b/src/extras/PMREMGenerator.js
index fe47c7b8292ee4dea2fa5de2f8e7a46fb3376181..5dcf3c475ac30c05bc0d9c6f1d5b456feffbcc4c 100644
--- a/src/extras/PMREMGenerator.js
+++ b/src/extras/PMREMGenerator.js
@@ -707,15 +707,12 @@ uniform vec2 texelSize;
 
 ${_getEncodings()}
 
-#define RECIPROCAL_PI 0.31830988618
-#define RECIPROCAL_PI2 0.15915494
+#include <common>
 
 void main() {
 	gl_FragColor = vec4(0.0);
 	vec3 outputDirection = normalize(vOutputDirection);
-	vec2 uv;
-	uv.y = asin(clamp(outputDirection.y, -1.0, 1.0)) * RECIPROCAL_PI + 0.5;
-	uv.x = atan(outputDirection.z, outputDirection.x) * RECIPROCAL_PI2 + 0.5;
+	vec2 uv = equirectUv( outputDirection );
 	vec2 f = fract(uv / texelSize - 0.5);
 	uv -= f * texelSize;
 	vec3 tl = envMapTexelToLinear(texture2D(envMap, uv)).rgb;
diff --git a/src/renderers/WebGLCubeRenderTarget.js b/src/renderers/WebGLCubeRenderTarget.js
index b4bdec6544728f41182a09072a2d6f2148fb158e..03277c2170a4794a04b19fbe2af6f4d7779f18ce 100644
--- a/src/renderers/WebGLCubeRenderTarget.js
+++ b/src/renderers/WebGLCubeRenderTarget.js
@@ -72,18 +72,13 @@ WebGLCubeRenderTarget.prototype.fromEquirectangularTexture = function ( renderer
 
 			"varying vec3 vWorldDirection;",
 
-			"#define RECIPROCAL_PI 0.31830988618",
-			"#define RECIPROCAL_PI2 0.15915494",
+			"#include <common>",
 
 			"void main() {",
 
 			"	vec3 direction = normalize( vWorldDirection );",
 
-			"	vec2 sampleUV;",
-
-			"	sampleUV.y = asin( clamp( direction.y, - 1.0, 1.0 ) ) * RECIPROCAL_PI + 0.5;",
-
-			"	sampleUV.x = atan( direction.z, direction.x ) * RECIPROCAL_PI2 + 0.5;",
+			"	vec2 sampleUV = equirectUv( direction );",
 
 			"	gl_FragColor = texture2D( tEquirect, sampleUV );",
 
diff --git a/src/renderers/shaders/ShaderChunk/common.glsl.js b/src/renderers/shaders/ShaderChunk/common.glsl.js
index fccf02d464f9bd7070d258543dd3ee798d8b93e3..947fd3c05ad2971dc6caba432749bb5cb3ab44b4 100644
--- a/src/renderers/shaders/ShaderChunk/common.glsl.js
+++ b/src/renderers/shaders/ShaderChunk/common.glsl.js
@@ -117,5 +117,17 @@ bool isPerspectiveMatrix( mat4 m ) {
 
   return m[ 2 ][ 3 ] == - 1.0;
 
+}
+
+vec2 equirectUv( in vec3 dir ) {
+
+	// dir is assumed to be unit length
+
+	float u = atan( dir.z, dir.x ) * RECIPROCAL_PI2 + 0.5;
+
+	float v = asin( clamp( dir.y, - 1.0, 1.0 ) ) * RECIPROCAL_PI + 0.5;
+
+	return vec2( u, v );
+
 }
 `;
diff --git a/src/renderers/shaders/ShaderChunk/envmap_fragment.glsl.js b/src/renderers/shaders/ShaderChunk/envmap_fragment.glsl.js
index 93b5d50686e133b5eb9cd5d7486c5cd7d8e92827..3b9d285f622e0308698e6875caf76779fb00a7e4 100644
--- a/src/renderers/shaders/ShaderChunk/envmap_fragment.glsl.js
+++ b/src/renderers/shaders/ShaderChunk/envmap_fragment.glsl.js
@@ -44,13 +44,9 @@ export default /* glsl */`
 
 	#elif defined( ENVMAP_TYPE_EQUIREC )
 
-		vec2 sampleUV;
-
 		reflectVec = normalize( reflectVec );
 
-		sampleUV.y = asin( clamp( reflectVec.y, - 1.0, 1.0 ) ) * RECIPROCAL_PI + 0.5;
-
-		sampleUV.x = atan( reflectVec.z, reflectVec.x ) * RECIPROCAL_PI2 + 0.5;
+		vec2 sampleUV = equirectUv( reflectVec );
 
 		vec4 envColor = texture2D( envMap, sampleUV );
 
diff --git a/src/renderers/shaders/ShaderChunk/envmap_physical_pars_fragment.glsl.js b/src/renderers/shaders/ShaderChunk/envmap_physical_pars_fragment.glsl.js
index 3fa872ae75dfc47040687617836d798122e5f4f3..53dfe149f0d995c1fdaf27c0465d38ae2b6d8458 100644
--- a/src/renderers/shaders/ShaderChunk/envmap_physical_pars_fragment.glsl.js
+++ b/src/renderers/shaders/ShaderChunk/envmap_physical_pars_fragment.glsl.js
@@ -97,9 +97,7 @@ export default /* glsl */`
 
 		#elif defined( ENVMAP_TYPE_EQUIREC )
 
-			vec2 sampleUV;
-			sampleUV.y = asin( clamp( reflectVec.y, - 1.0, 1.0 ) ) * RECIPROCAL_PI + 0.5;
-			sampleUV.x = atan( reflectVec.z, reflectVec.x ) * RECIPROCAL_PI2 + 0.5;
+			vec2 sampleUV = equirectUv( reflectVec );
 
 			#ifdef TEXTURE_LOD_EXT
 
diff --git a/src/renderers/shaders/ShaderLib/equirect_frag.glsl.js b/src/renderers/shaders/ShaderLib/equirect_frag.glsl.js
index 52269daba1b8daca6d1af3deb8b8cfbf96b36590..0bb0e0611186ce89452c2c121913d8f7b774f92c 100644
--- a/src/renderers/shaders/ShaderLib/equirect_frag.glsl.js
+++ b/src/renderers/shaders/ShaderLib/equirect_frag.glsl.js
@@ -9,11 +9,7 @@ void main() {
 
 	vec3 direction = normalize( vWorldDirection );
 
-	vec2 sampleUV;
-
-	sampleUV.y = asin( clamp( direction.y, - 1.0, 1.0 ) ) * RECIPROCAL_PI + 0.5;
-
-	sampleUV.x = atan( direction.z, direction.x ) * RECIPROCAL_PI2 + 0.5;
+	vec2 sampleUV = equirectUv( direction );
 
 	vec4 texColor = texture2D( tEquirect, sampleUV );