Body mass index (BMI) is commonly used for assessing body fat. Self-reported body weight and height derived BMI (SRDBMI) is a simple, low cost and non-invasive assessment tool and it may be a useful self-reported assessment tool to monitor the prevalence of overweight/obesity in community settings and for epidemiological research. We assessed the agreement of BW and BH between assessor measured and child self-reported values and evaluated the diagnostic ability of SRDBMI to identify children with overweight/obesity status and cardiometabolic risk factors (CMRFs) clustering. A cross-sectional study was conducted in school settings using a cluster sampling method. A total of 1,614 children aged 6-18 years were included in the analysis. Children were given a questionnaire to complete at home prior to the anthropometric measurements and blood taking at the schools. There was almost perfect agreement on BW, BH and BMI between self-reported and measured values [intraclass correlation coefficients ranged from 0.93 (95% CI: 0.93-0.94) to 0.99 (95% CI: 0.98-0.99)]. About half of the children reported their BW and BH absolute values within 1 kg and 2 cm of measured values, respectively. The SRDBMI demonstrated good diagnostic ability for identifying children with overweight/obesity status (sensitivity, specificity, positive and negative predictive values ranged from 0.83 to 0.98) and CMRFs clustering (AUC-ROCs values of BMI between measured and self-reported values were close ranging from 0.85 to 0.89). Self-reported BW and BH demonstrated almost perfect agreement with measured values and could substantially identify children with overweight/obesity status and CMRFs clustering.