Quantitative　phase　analysis　is　one　of　the　major　applications　of　X-ray　powder　diffraction.　The　essential　principle　of　quantitative　phase　analysis　is　that　the　diffraction　intensity　of　a　component　phase　in　a　mixture　is　proportional　to　its　abundance.　Nevertheless,　the　diffraction　intensities　of　the　component　phases　cannot　be　compared　with　each　other　directly　since　the　coherent　scattering　power　per　unit　cell　(or　chemical　formula)　of　each　component　phase　is　usually　different.　The　coherent　scattering　power　per　unit　cell　of　a　crystal　is　well　represented　by　the　sum　of　the　squared　structure　factors,　which　cannot　be　calculated　directly　when　the　crystal　structure　data　is　unavailable.　Presented　here　is　a　way　to　approximate　the　coherent　scattering　power　per　unit　cell　based　solely　on　the　unit　cell　parameters　and　the　chemical　contents.　This　approximation　is　useful　when　the　atomic　coordinates　for　one　or　more　of　the　phases　in　a　sample　are　unavailable.　An　assessment　of　the　accuracy　of　the　approximation　is　presented.　This　assessment　indicates　that　the　approximation　will　likely　be　within　10%　when　X-ray　powder　diffraction　data　is　collected　over　a　sufficient　portion　of　the　measurable　pattern.