Cereal crop Zn biofortification is an effective solution to global human Zn deficiency and is achieved by increasing grain Zn concentration concurrently with yield. However, the desired grain Zn concentration (>40 mg kg^-1) is rarely observed for high-yielding wheat on calcareous soils, owing to inadequate Zn uptake or Zn distribution to grain. This study was designed to determine how much Zn uptake or distribution is adequate for Zn biofortification, by considering 123 bread wheat (Triticum aestivum L.) cultivars grown on calcareous soils with low available Zn (=0.5 mg kg^-1) in the field on the southern Loess Plateau, China. Nineteen high-yielding cultivars were identified with similar yields (∼7.0 t ha^-1) and various grain Zn concentrations from 9.3 to 26.7 mg kg^-1. Adequate Zn distribution to grain was defined as the situation where the Zn harvest index at maturity increased to its maximum of ∼91.0% and straw Zn concentration at maturity decreased to its minimum of ∼1.5 mg kg^-1. For each cultivar, the extra Zn in straw above the minimum could be again remobilised to grain and raise grain Zn concentration to its highest attainable level, which was 14.5–31.3 mg kg^-1 for the 19 high-yielding cultivars but still =40 mg kg^-1. Thus, the current Zn uptake needs to be increased to ≥308 g ha^-1 to achieve Zn biofortification on low-Zn calcareous soils. For other wheat production regions, the method established here can also provide the priority measures and quantitative guidelines for Zn biofortification.