Objectives: Ulnar variance is a clinical measure used to determine the relative difference in length between the radius and ulna. We aimed to examine consistency in ulnar variance measurements and normative data in children and adolescents using the perpendicular and the Hafner methods. Methods: Two raters measured ulnar variance on hand radiographs of 350 healthy children. Participants’ mean calendar and skeletal ages were 12.3 ± 3.6 and 12.0 ± 3.7 years, 52% were female. Raters used the perpendicular method, an adapted version of the perpendicular method (in which the distal radial articular surface is defined as a sclerotic rim) and the Hafner method, being the distance between the most proximal points of the ulnar and radial metaphyses (PRPR) and the distance between the most distal points of both (DIDI). Intraclass correlation coefficients (ICCs) for intermethod consistency and inter- and intrarater agreement were calculated using a two-way ANOVA model. Variability and limits of agreement were determined using the Bland-Altman method. Results: The interrater ICC was 0.75 (95% CI, 0.61–0.84) for the adapted perpendicular method, 0.88 (95% CI, 0.80–0.93) for PRPR, and 0.94 (95% CI, 0.90–0.97) for DIDI. The intermethod consistency ICC was 0.60 (95% CI, 0.48–0.70) for perpendicular versus PRPR and 0.60 (95% CI, 0.49–0.70) for perpendicular versus DIDI. The intrarater ICC was 0.88 (95% CI, 0.70–0.95) for perpendicular, 0.90 (95% CI, 0.83–0.94) for PRPR, and 0.81 (95% CI, 0.69–0.89) for DIDI. The perpendicular method was not useable in 38 cases (skeletal age ≤ 9 years) and the Hafner method in 79 cases (skeletal age ≥ 12 years). Conclusions: The perpendicular and Hafner methods show moderate intermethod consistency. The Hafner method is preferred for children with skeletal ages < 14 years, with good to excellent inter- and intrarater agreement. The adapted perpendicular method is recommended for patients with skeletal ages ≥ 14 years. Key Points: • The perpendicular method for measuring ulnar variance requires extended instructions to ensure good interrater agreement in pediatric and adolescent patients. • The Hafner method is recommended for ulnar variance measurement in children with unfused growth plates and up to a skeletal age of 13 years, and the perpendicular method is recommended for children with fused growth plates and from skeletal age 14 and older. • The mean ulnar variance measured in this study for each skeletal age group (range, 5–18 years) is provided, to serve as a reference for future ulnar variance measurements using both methods in clinical practice.