Blue litmus paper turns red at pH 4.5 or less (acidic). Red litmus paper turns blue at pH 8.3 or more (basic). Neutral litmus paper turns from purple to blue or red. Strips measure 7 x 48 mm.

Blue litmus paper turns red at pH 6.5 or less (acidic). Red litmus paper turns blue at pH 8.3 or more (basic). Neutral litmus paper turns from purple to blue or red. Strips measure 7 x 48 mm.

Note: Not for measuring the pH of natural waters, such as streams, rivers, and lakes. To measure pH in these waters, try pH and Total Alkalinity Water Test Strip, pH 6-9 (item #652729), or for a wider pH range, LaMotte® Wide-Range pH Water Test Kit, pH 3.0-10.5 (item #652927).