Small-angle X-ray scattering (SAXS) patterns are used to identify features of semicrystalline polymers composed of alternating lamellar crystals and amorphous regions. Provided that lamellae are wide and flat, the structure is a one-dimensional stack with an average periodLestablished by distributions of crystal thicknessH(y) and amorphous thicknessh(z) and with crystallinity α = [ybar]/[xbar], where average crystal thickness is [ybar], and average long period is [xbar]. The one-dimensional intensityI1(s1) givesLB, while the one-dimensional correlation function γ1(r) and the one-dimensional interface distribution functiong1(r) also provide measures of periodicityr*andr3, respectively. Obvious features of γ1(r) andg1(r) also permit estimation of crystallinity, designated αγand αgrespectively.I1(s1), γ1(r) andg1(r) are calculated for models having symmetric and positively skewed distributionsH(y) andh(z) and for stacks of finite heightN[xbar]. For all conditions, it is found thatLB≥r*≥r3, and that αg≥ α ≥ αγ. With symmetric distributions and infiniteN,LBnearly equals the weight-average period [xbar]w, andr3= [xbar]. These equalities do not hold when thickness distributions are skewed. Small stack heightN[xbar] distortsI1(s1) and γ1(r), but the interface distribution functiong1(r) is scarcely affected, returningr3= [xbar] and αg= α. It is recommended that all three functions be analyzed to obtain the most complete picture of the semicrystalline microstructure.