According to Jentz (JENTZ, Thomas L.; Germany's TIGER Tanks - Tiger I and II: Combat Tactics; op. cit.), "The Tiger's armor was invulnerable to attack from most tank guns firing normal armor-piercing shells or shot at ranges over 800 meters, including the American 75 mm and the Russian 76 mm. It is obvious that the 17-pdr. firing normal APCBC rounds could defeat the frontal armor of the Tiger I at most combat ranges for tank vs. tank actions in Europe. However, by 23 June 1944, only 109 Shermans with 17-pdrs. had landed in France along with six replacements. By the end of the war, on 5 May 1945, the British 21st Army Group possessed 1,235 Sherman tanks with 17-pdrs., while the remaining 1,915 Sherman tanks were all equipped with the 75 mm M3 gun".
The Tiger I armor could take a lot of punishment, as can be seen by the number of hits taken by Tiger 312. One of the Tigers from 2.Kompanie, sPzAbt.504, lost in the first days following the Allied landings on Tunisia on 10 July 1943.
The armor of the Tiger I was not well sloped, but it was thick. Here is where many fail to understand that, in terms of World War II tank warfare, thickness was a quality in itself, since armor resistance is mainly determined by the ratio between armor thickness and projectile diameter (T/d). The T/d relationship regarding armor penetration demonstrates that the more the thickness of the armor plate overmatches the diameter of any incoming armor piercing round, the harder it is for the projectile to achieve a penetration. On the other side, the greater the diameter of the incoming projectile relatively to the thickness of the armor plate which it strikes, the greater the probability of penetration. This explains why the side armor of the Tiger I, being 80 mm thick, was so difficult to be penetrated at combat ranges by most Allied anti-tank and tank guns, whose calibers were overmatched by the thickness of the Tiger I armor.
The rolled homogeneous nickel-steel plate, electro-welded interlocking-plate construction armor had a Brinell hardness index of around 255-280 (the best homogeneous armor hardness level for the corresponding thickness level of the Tiger's armor, by WW II standards), and rigorous quality control procedures ensured that it stayed that way. About this issue, and according to Thomas L. Jentz, "there is no proof that substandard german armour plate was used during the last years of the war. All original documents confirm compliance with standard specifications throughout the war" (JENTZ, Thomas L. Germany's TIGER Tanks, VK45.02 to Tiger II: Design, Production Modifications).
Moreover, in the same reference book, Jentz presents the data from a British testing of the Tiger's armor protection by firing different guns against it. The tests were realized in a place beside the the main road from Beja to to Sidi N'sir in Tunisia, on May 19, 1943. The reports from these tests stated that the resistance of the Tiger's armor was "considerably higher than that of the British machineable quality armor. The side armor, with a thickness of 82 mm (nominal thickness was 80 mm) had a resistance equivalent of 92 mm of British armor" (Jentz, op cit, page 15). However, a little further, when addressing directly the issue of the Tiger's armor quality, the report states that "The armor plates (with exception of the hull roof plates) did not show any marked tendency to brittleness, and their behavior generally was not unlike British mechineable plates. The following table gives a list of Poldi hardness, corrected to Brinell figures, taken at the surface of the armor".
Armor Nominal Thickness Brinell Hardness No.
Turret Roof 25 mm 290
Hull Roof 25 mm 335
Glacis 60 mm 265
Hull Sides 60 mm 265
Turret Sides 80 mm 255
Superstructure 80 mm 260-255
Hull Rear 80 mm 255
Driver's Front Plate 100 mm 265
Hull Front 100 mm 265
Mantlet 100-200 mm 280
NOTE: Actually, the Tiger I chassis Nbr. 250570, object of the trials, was assembled in early October 1943, and its armor would have been rolled, cut, hardened, and welded together at least three months earlier - that is, before July 1943.
The Tiger, as a result of it's intrinsic doctrinal mission - that is, to effect a breakthrough and to support medium tanks, during the breakthrough, by destroying enemy tanks - was, production-wise, a very expensive and resource consuming tank. The nominal cost of a Tiger was 250,800 Reichsmarks. In contrast, a PzKpfw III Ausf. M cost RM 103,163, a PzKpfw IV Ausf. G RM 115,962, and a PzKpfw V Panther RM 117,100; all these figures are exclusive of weapons and radios. However, the final cost of the Tiger's production was even higher - 299,800 Reichsmarks (Source: HAHN, Fritz. Waffen und Geheimwaffen des deutschen Heeres 1933-1943 Band 1 Band 2. Koblenz : Bernard Graefe Verlag, 1987, in Christian Ankerstjerne's Panzerworld web site. Accessed in June 21, 2007).
Christopher W. Wilbeck, in "Sledgehammers: Strengths and Flaws of Tiger Heavy Tank Battalions in World War II", citing the Tigerfibel (the Tiger's manual), states that the final cost of the Tiger's production was much higher - 800,000 Reichsmarks - and 300,000 man-hours were required to produce one single Tiger. The Tigerfibel , in view of making those numbers more personal to the Tiger crewmen, stated that it was required one week of hard work from 6,000 people to produce one Tiger. It also stated that 800,000 Reichsmarks figure was equivalent to the weekly wages for 30,000 people.
The frontal vertical plating was massive enough to withstand virtually anything. Tiger I disabled by a side penetration that hit the engine and caused the suspension to collapse.
Another fact that helped the Tigers a lot was the "shatter gap" effect which affected allied ammunition, a most unusual situation where rounds with too high an impact velocity would sometimes fail even though their penetration capability was (theoretically) more than adequate. This phenomenon plagued the British 2 pounder in the desert, and would have decreased the effectiveness of U.S. 76mm and 3" guns against Tigers, Panthers and other vehicles with armor thickness above 70 mm. It should be noted that the problems with the 76 mm and 3" guns did not necessarily involve the weapons themselves: the noses of US armor-piercing ammunition of the time turned out to be excessively soft. When these projectiles impacted armor which matched or exceeded the projectile diameter at a certain spread of velocities, the projectile would shatter and fail.
Penetrations would occur below this velocity range, since the shell would not shatter, and strikes above this range would propel the shell through the armor whether it shattered or not. When striking a Tiger I driver's plate, for example, this "shatter gap" for a 76mm APCBC M62 shell would cause failures between 50 meters and 900 meters. These ammunition deficiencies proved that Ordnance tests claiming the 76 mm gun could penetrate a Tiger I's upper front hull to 2,000 yards (1,800 meters) were sadly incorrect.
As a general rule, BHN (Brinell Hardness Index) effects, shot shatter, and obliquity effects are related to the ratio between shot diameter and plate thickness. The relationship is complex, but a larger projectile hitting relatively thinner plate will usually have the advantage. There is an optimum BHN level for every shot vs plate confrontation, usually in the 260-300 BHN range for World War Two situations. Below that, the armor is too soft and resists poorly, above that, the armor is too hard and therefore too brittle.