The flag of Brazil is covered in Law 5700 of 01 September, 1971 and modified by Law 8421 of 11 May, 1992.

Law 8421 of 11 May, 1992

ART. 3 - The National Flag, adopted by Decree no. 4, of November 19, 1889, with the modifications of Law no. 5,443, of May 28, 1968, is altered in the form of Annex I of this law, and must be updated whenever the creation or extinction of States occurs.

1. The constellations that appear on the National Flag correspond to the aspect of the sky, in the city of Rio de Janeiro, at 8:30 am on November 15, 1889 (twelve sidereal hours) and should be considered as seen by an observer located outside the celestial sphere.
2. The new States of the Federation will be represented by stars that make up the celestial aspect referred to in the previous paragraph, in order to allow them to be included in the blue circle of the National Flag without affecting the original aesthetic arrangement contained in the design proposed by Decree no. 4, of November 19, 1889.
3. The stars corresponding to the extinct States will be removed from the National Flag, remaining the one designated to represent the new State, resulting from merger, observing, in any case, the provisions in the final part of the previous paragraph. [Law 8421 of 11 May, 1992]

Law 5700 of 01 September, 1971

ART. 5 - The construction of the national flag will conform to the following rules.

1. To calculate the dimensions, take as a basis the desired width [of the hoist] and divide it into 14 (fourteen) equal parts. Each of these parts will be considered a measure or module, M.
2. The length [of the fly] will be 20 modules (20 M).
3. The distance from the vertices of the yellow lozenge to the edge of the field will be one and seven tenths modules (1.7 M).
4. The blue circle in the middle of the lozenge will have a radius of three and a half modules (3.5 M).
5. The center of the arcs of the white band will be two modules (2 M) to the left of the point where the extension of the vertical diameter of the circle meets the lower edge of the field (point C indicated in Annex number 2).
6. The radius of the lower arc of the white band will be eight modules (8 M); the radius of the upper arc of the white band will be eight and a half modules (8.5 M).
7. The width of the white band will be one-half module (0.5 M).
8. The letters of the motto "Ordem e Progresso" will be in green. They will be located in the middle of the white stripe, with equal white spaces above and below. The letter P will be placed on the vertical diameter of the circle. The distribution of the other letters will be as indicated in Annex number 2. The letters of the word "Ordem" and of the word "Progresso" will be one-third of a module (0.333 M) in height. The width of these letters will be three-tenths of a module (0.3 M). The height of the letter of the conjunction "E" will be three-tenths of a module (0.3 M). The width of this letter will be one quarter of a module (0.25 M).
9. The stars will be in 5 (five) dimensions: of the first, second, third, fourth, and fifth sizes. They are to be traced within circles whose dimensions will be: three-tenths of a module (0.3 M) for the first size; one-quarter of a module (0.25 M) for the second size; one-fifth of a module (0.2 M) for the third size; one-seventh of a module (0.143 M) for the fourth size; and one-tenth of a module (0.1 M) for the fifth size.
10. The two sides [of the flag] will be exactly equal, with the white stripe inclined from left to right (from the point of view of an observer facing the flag), it being forbidden to make one side as a mirror-image of the other. [Law 5700 of 01 September, 1971]