delivered the opinion of the Court.
An act of the legislature of Nebraska, approved March 31,1921 (Laws 1921, c. 2, p. 56)1 provides that every loaf of bread made for the purpose of sale, or offered for sale, or sold, shall be one-half pound, one pound, a pound and a half, or exact multiples of one pound, and prohibits loaves of other weights. It allows a tolerance in excess of the specified standard weights at the rate of two ounces per pound *511and no more, and requires that the specified weight shall be the average weight of not less than 25 loaves, and that such average shall not be more than the maximum nor less than the minimum prescribed. Violations of the act are punishable by a fine or imprisonment.
Four of the plaintiffs in error are engaged in Nebraska in the business of baking and selling bread for consumption there and in other States. Their total annual output is alleged to be 23,500,000 pounds. The other plaintiff in error is a retail grocer at Omaha, and sells bread to consumers principally in single loaf lots. They brought this suit against the Governor and the Secretary of the Department of Agriculture of the State to restrain the enforcement of the act on the ground, among others, that it is repugnant to the due process clause of the Fourteenth Amendment. The State Supreme Court sustained the act. The case is here on writ of error.
Plaintiffs in error do not question the power of the State to enact and enforce laws calculated to prevent the sale of loaves of bread of less than the purported weight; but they contend that the provision fixing the maximum weights in this statute is unnecessary, unreasonable and arbitrary.
*512The brief of the Attorney General states that the law is concerned with weights only. The State Supreme Court said (108 Nebr. 674, 678): “ It is to prevent a loaf of one standard from being increased in size until it can be readily sold for a loaf of a larger standard that a maximum weight is fixed. The test is reasonableness. . . . (p.679.) The statutory margin or tolerance being two ounces to the pound, can bakers, for example, make a loaf 18 ounces in weight that will weigh not less than 16 ounces 24 hours after it is baked? The tests and proofs on behalf of the State tend to show that the regulation is reasonable and can be observed at all times. [In most of these tests, wrapped loaves were used.] It is fairly inferable from the evidence adduced by plaintiffs that compliance with the regulation is practicable most of the time, but that tested by their experiments as made, there are periods when the operation of natural laws will prevent compliance with legislative requirements. There are a number of reasons, however, why the tests made to prove unreasonableness should not be accepted as conclusive. If correctly understood, these tests were made with bread manufactured in the regular course of business, without any attempt to change ingredients or processes or to retard evaporation of moisture in loaves by the use of wax-paper or other means. . . . (p. 680.) The act of the legislature does not fix prices but leaves bakers free to make reasonable charges for bread wrapped in inexpensive wax-paper for its preservation in transportation and in the markets. . . . Precautions to retard evaporation of moisture in bread for the purpose of keeping it in a good state of preservation for 24 hours may be required as an incidental result of a police regulation establishing standards of maximum weights for loaves of bread. Palatableness, a quality demanded by the public, is affected by excessive evaporation, if food value is not. . . . The evidence does not prove that, if reasonable means or precautions are taken by plaintiffs *513and other bakers to retard evaporation, they cannot comply with the act of the legislature, or that the regulation is unreasonable.”
Undoubtedly, the police power of the State may be exerted to protect purchasers from imposition by sale of short weight loaves. Schmidinger v. Chicago, 226 U. S. 578, 588. Many laws have been passed for that purpose. But a State may not, under the guise of protecting the public, arbitrarily interfere with private business or prohibit lawful occupations or impose unreasonable and unnecessary restrictions upon them. Lawton v. Steele, 152 U. S. 133, 137; Meyer v. Nebraska, 262 U. S. 390, 399. Constitutional protection having been invoked, it is the duty of the court to determine whether the challenged provision has reasonable relation to the protection of purchasers of bread against fraud by short weights and really tends to accomplish the purpose for which it was enacted. Meyer v. Nebraska, supra; Welch v. Swasey, 214 U. S. 91, 105; Dobbins v. Los Angeles, 195 U. S. 223, 236; Connolly v. Union Sewer Pipe Co., 184 U. S. 540, 556; Lawton v. Steele, supra.
The loaf is the usual form in which bread is sold. The act does not make it unlawful to sell individual loaves weighing more or less than the standard weights respectively. Loaves of any weight may be sold without violation of the act, if the average weight of not less than 25 does not exceed the permitted maximum or fall short of the specified nominal weights during 24 hours after baking. Undoubtedly, very few private consumers purchase at one time as many as 25 loaves of the same standard size or unit. And it is admitted that the sale of a lesser number not within the permitted tolerance does not constitute an offense. Plaintiffs in error do not claim that it is impossible to make loaves which for at least 24 hours after baking will weigh not less than the specified minimum weights, but they insist that the difference per*514mitted by the act between the weight of loaves when taken from the oven and their weight 24 hours later is too small, and that it is impossible for bakers to carry on their business without sometimes exceeding the maximum or falling short of the minimum average weights. Any loaves of the same unit at any time on hand during 24 hours after baking may be selected to make up the 25 or more to be weighed in order to test compliance with the act. Therefore, if only a small percentage of the daily output of the loaves in large bakeries shall exceed the maximum when taken from the oven or fall below the minimum weight within 24 hours, it will always be possible to make up lots of 25 or more loaves whose average weight will be above or below the prescribed limits.
The parties introduced much evidence on the question whether it is possible for bakers to comply with the law. A number of things contribute to produce unavoidable variations in the weights of loaves at the time of and after baking. The water content of wheat, of flour, of dough2' and of bread immediately after baking varies substantially and is beyond the control of bakers. Gluten is an important element in flour, and flour rich in gluten requires the addition of more water in breadmaking and malees better bread than does flour of low or inferior gluten content. Exact weights and measurements used *515in doughmaking cannot be attained. Losses in weight while dough is being mixed, during fermentation and while the bread is in the oven, vary and cannot be avoided or completely controlled. No hard and fast rule or formula is followed in breadmaking. There are many variable elements. Bread made from good flour loses more weight by evaporation of moisture after baking than does bread made from inferior flours. Defendants’ tests were made principally with loaves which were wrapped so as to retard evaporation; and it was shown that by such wrapping the prohibited variations in weight may be avoided. On the other hand, the evidence clearly establishes that there are periods when evaporation under ordinary conditions of temperature and humidity prevailing in Nebraska exceeds the prescribed tolerance and makes it impossible to comply with the law without wrapping the loaves or employing other artificial means to prevent or retard evaporation. And the evidence indicates that these periods are of such frequency and duration that the enforcement of the penalties prescribed for violations would be an intolerable burden upon bakers of bread for sale. The tests which were described in the evidence and referred to in the opinion are not discredited because “ made with bread manufactured in the regular course of business.” The reasonableness of the regulation complained of fairly may be measured by the variations in weight of bread so made. The act does not require bakers to select ingredients or to apply processes in the making of bread that will result in a product that will not vary in weight during 24 hours after baking as much as does bread properly made by the use of good wheat flour. As indicated by the opinion of the State Supreme Court, ingredients selected to lessen evaporation after baking would make an inferior and unsalable bread. It would be unreasonable to compel the making of such a product or to prevent making of good bread in order to comply *516with the provisions of the act fixing maximum weights. The act is not a sanitary measure. It does not relate to the preservation of bread in transportation or in the market; and it applies equally whether the bread is sold at the bakeries or is shipped to distant places for sale. Admittedly, the provision in question is concerned with weights only. The act does not regulate moisture content or require evaporation to be retarded by the wrapping of loaves or otherwise. The uncontradicted evidence shows that there is a strong demand by consumers for unwrapped bread. It is a wholesome article of food, and plaintiffs in error and other bakers have a right to furnish it to their customers. The lessening of weight of bread by evaporation during 24 hours after baking does not reduce its food value. It would be unreasonable to prevent unwrapped bread being furnished to those who want it in order technically to comply with a weight regulation and to keep within limits of tolerance so narrow as to require that ordinary evaporation be retarded by wrapping or other artificial means. It having been shown that during some periods in Nebraska bread made in a proper and usual way will vary in weight more than at the rate of two ounces to the pound during 24 hours after baking, the enforcement of the provision necessarily will have the effect of prohibiting the sale of unwrapped loaves when evaporation exceeds the tolerance'.
No question is presented as to the power of the State to make regulations safeguarding or affecting the qualities of bread. Concretely, the sole purpose of fixing the maximum weights, as held by the Supreme Court, is to prevent the sale of a loaf weighing anything over nine ounces for a one pound loaf, and the sale of a loaf weighing anything over eighteen ounces for a pound and a half loaf; and so on. The permitted tolerance, as to the half pound loaf, gives the baker the benefit of only one ounce *517out of the spread of eight ounces, and as to the pound loaf the benefit of only two ounces out of a like spread. There is no evidence in support of the thought that purchasers have been or are likely to be induced to take a nine and a half or a ten ounce loaf for a pound (16 ounce) loaf, or an eighteen and a half or a 19 ounce loaf for a pound and a half (24 ounce) loaf; and it is contrary to common experience and unreasonable to assume that there could be any danger of such deception. Imposition through short weights readily could have been dealt with in a direct and effective way. For the reasons stated, we conclude that the provision, that the average weights shall not exceed the máximums fixed, is not ^necessary for the protection of purchasers against imposition and fraud by short weights and is not calculated to effectuate that purpose, and that it subjects bakers and sellers of bread to restrictions which are essentially unreasonable and arbitrary, and is therefore repugnant to the Fourteenth Amendment.
Judgment reversed.
An Act establishing a standard weight loaf of bread for the State of Nebraska and providing a penalty. . . .
Section 1. Department of agriculture to enforce. — It shall be the duty of the Department of Agriculture to enforce all provisions of this Act. It shall make or cause to be made all necessary examinations and shall have authority to promulgate such rules and regulations as are necessary to promptly and effectively enforce the provisions of this Act.
Sec. 2. Bread, standards of weight. — Every loaf of bread made or procured for the purpose of sale, sold, exposed or offered for sale in the State of Nebraska shall be the following weights avoirdupois, one-half pound, one pound, one and one-half pounds, and also in exact multiples of one pound and of no other weights. Every loaf of bread shall be made of pure flour and wholesome ingredients and shall be free from any injurious or deleterious substance. Whenever twin or multiple loaves are baked, the weights herein specified shall apply to each unit of the twin or multiple loaf.
See. 3. Tolerance, how determined. — A tolerance at the rate of two ounces per pound in excess of the standard weights herein fixed shall be allowed and no more, provided that the standard weights herein prescribed shall be determined by averaging the weight of not less than twenty-five loaves of any one unit and such average shall not *511be less than the minimum nor more than the maximum prescribed by this Act. All weights shall be determined on the premises where bread is manufactured or baked and shall apply for a period of at least twenty-four hours after baking. Provided, that bread shipped into this state shall be weighed where sold or exposed for sale.
Sec. 4. Penalties for violation. — Any person, firm or corporation violating any of the provisions of this Act, shall be punished by a fine of not less than ten dollars nor more than one hundred dollars or by imprisonment in the county jail for not more than thirty days. Provided, however, that upon the second and all subsequent convictions for the violation of any of the provisions of this Act such offender shall be punished by a fine of not less than fifty dollars nor more than one hundred dollars, or by imprisonment in the county jail for not more than ninety days.
Wheat bread dough is the dough consisting of a leavened and kneaded mixture of flour, potable water, edible fat or oil, sugar and / or other fermentable carbohydrate substance, salt, and yeast, with or without the addition of milk or a milk product, of diastatic and / or proteolytic ferments, and of such limited amounts of unobjectionable salts as serve solely as yeast nutrients, and with or without the replacement of not more than three per cent of the flour ingredient by some other edible farinaceous substance. (Definition of Joint Committee on Definitions and Standards, September 28, 1922, and approved by the Association of American Dairy Food and Drug Officials, October 5, 1922, and by the Association of Official Agricultural Chemists, November 17, 1922.)