Abstract The stability of thin plates has been investigated by many authors. However, in aeronautical structures, thin metal sheets are often used beyond the stability limits, and the load which can be carried by the structure is determined by the ultimate strength in compression. A recent series of experiments by the Bureau of Standards showed the ultimate load to be independent of width and length of the plate and approximately proportional to the square of the thickness. In the present paper an approximate theoretical analysis of this problem is developed, by which the “effective width” and the ultimate strength can be found. The result of this analysis shows the ultimate strength of a plate to be proportional to the square roots of the modulus of elasticity and the yield point of the material, and to the square of the thickness. This result gives a good check with the experiments mentioned.