This study is intended to determine the knowledge in length unit conversion among Grade 7 students. This study was conducted to determine the significant difference between the pre-test and post-test scores of the students in employing mnemonics in unit length conversion. A pre-experimental research design was utilized to measure the effect of the intervention. Data were gather from 35 Grade 7 students at Baltazar Nicor Valenzuela National High School, selected through purposive sampling. Data collection was done through pre-test and post-test administration. Findings revealed a substantial difference in the scores before and after the intervention. The mean pre-test score was 14.55% (Poor), while the mean post-test score was 63% (Satisfactory). The paired t-test results indicated a significant improvement in students' scores from the pre-test to the post-test, with t (35) = 16.91, p < .001. This substantial difference suggests a strong effect of the intervention on students' ability to mnemonics, indicating a highly significant and positive impact on their computational fluency. To provide a comprehensive understanding of the students' experiences, the researchers conducted in-depth interviews with selected participants. From their responses, nine themes was identified from the insights of students: Mnemonics Clarify the Process of Solving in Conversions, Mnemonics Make Unit Conversion Less Confusing, Use of First Letter and Order of Words Provides Clarity, Keywords Serve as Reference Points for Specific Units, Difficulty in Remembering Specific Words or Their Meaning, Use of Visual Aids in Found More Effective, Use of Rhythm for Easier Memorization, Mnemonics Boosted Student’s Confidence, and Mnemonics Increased Students’ Learning Motivation. It can be concluded that the implementation of the mnemonics was helpful to the performance of the students in mastery in length unit conversion. Since there is a significant relationship between the implementation of mnemonics before and after the implementation of intervention.