diff --git a/sys/include/phydat.h b/sys/include/phydat.h
index 0ab28226ff..b94aecb8a4 100644
--- a/sys/include/phydat.h
+++ b/sys/include/phydat.h
@@ -104,6 +104,7 @@ enum {
     UNIT_PERCENT,   /**< out of 100 */
     UNIT_PERMILL,   /**< out of 1000 */
     UNIT_PPM,       /**< part per million */
+    UNIT_PPB,       /**< part per billion */
     /* aggregate values */
     UNIT_TIME,      /**< the three dimensions contain sec, min, and hours */
     UNIT_DATE       /**< the 3 dimensions contain days, months and years */
diff --git a/sys/phydat/phydat_str.c b/sys/phydat/phydat_str.c
index 3f17c2940a..7d5755c35d 100644
--- a/sys/phydat/phydat_str.c
+++ b/sys/phydat/phydat_str.c
@@ -95,6 +95,7 @@ const char *phydat_unit_to_str(uint8_t unit)
         case UNIT_BAR:      return "Bar";
         case UNIT_PA:       return "Pa";
         case UNIT_PPM:      return "ppm";
+        case UNIT_PPB:      return "ppb";
         case UNIT_CD:       return "cd";
         case UNIT_PERCENT:  return "%";
         default:            return "";