The composition of high‐quality single‐crystal bulk‐grown Cd1−yZnyTe (0≤y≤0.2) was determined from precision lattice constant measurements for a total of 22 data points. These samples were used to develop calibration curves for an accurate, contactless, nondestructive optical determination of composition using either 300 K transmission measurements or 77 K photoluminescence measurements. The 300 K transmission technique is useful for bulk CdZnTe wafers while the 77 K PL technique is applicable to both bulk and thin‐film CdZnTe. Both techniques are useful in determining Cd1−yZnyTe composition in the range (0≤y≤0.2) which covers the range needed for lattice‐matching to Hg1−xCdxTe and Hg1−xZnxTe epitaxial layers. The ability to map sample composition with high precision is available with both techniques.