Displayed pack prices versus standardized unit prices in Riyadh online supermarkets: implications for public health price monitoring

Background Online supermarket price comparisons can change when products are assessed by displayed pack price rather than a common quantity denominator. Methods This cross-sectional digital food-environment audit examined seven anonymized supermarkets’ official e-commerce websites serving Riyadh, Saudi Arabia. The category-level dataset comprised 241 rows representing 24,521 displayed items. A purposively constructed item-level subset preserved coverage across major food and beverage groups; 505 records were reviewed, 503 had a visible price, and 489 had complete and internally consistent price and package-size information for verified conversion to SAR/100 g or SAR/100 mL. The same 489 records were used to summarize pack price, package size, and standardized unit price by healthfulness. Secondary log-linear regressions used HC3 robust standard errors. Results Nutrient-poor categories had a lower item-count-weighted mean displayed pack price than nutrient-dense categories (14.62 vs. 18.30 SAR), although category medians were similar. Within the same item-level sample, nutrient-poor solids had a lower median pack price (11.63 vs. 12.95 SAR), a smaller median package size (150 vs. 520 g), and a higher median standardized price (7.75 vs. 2.49 SAR/100 g) than nutrient-dense solids. Nutrient-poor liquids showed the same descriptive pattern (4.93 vs. 8.50 SAR/pack; 250 vs. 1,000 mL; 1.97 vs. 0.85 SAR/100 mL). In adjusted models, nutrient-poor categories did not show a clear difference in displayed pack price relative to nutrient-dense categories (−4.3%; 95% CI, −21.8 to 17.2%; p = 0.673), whereas nutrient-poor solid items had a higher standardized unit price (+157.3%; 95% CI, 76.5 to 274.9%; p < 0.001). Conclusion Pack price and standardized unit price provide complementary views of digital retail prices. In this Riyadh snapshot, smaller typical package sizes among nutrient-poor items accompanied lower pack prices but higher prices per standardized quantity. These findings concern price measurement and monitoring and do not establish affordability, purchasing, or annual market effects.