T-34/76 front plate: 45 mm/60° = 90 mm effective armour
Sherman M4A3 front plate: 51 mm/56° = 91,2 mm effective armour
PzKpfw IV Ausf. H front plate: 80 mm/9° = 81 mm effective armour
I'am affraid it is not that simple.
Not the actual slope of the armor counts but the impact angle of the shell. Just because a plate of armour is sloped 60° from the vertical doesn't mean a shell will hit like that.
The effect of slop is usually much over exagerated in popular sources. It only works under certain conditions and usually not to the same degree as theory suggests.
Material quality plays a much bigger role for example. But it can't be seen on a picture. A layman also doesn'T know the difference between a face hardened rolled steel plate and a cast steel plate. HB230 is that good or bad? What is the difference between face hardened, thorough hardened or mild steel. What is more important hardness or elasticity? etc
This is not only true for the armor plate but also for the shell. A shell will penetrate better against lower quality armor. Mistakes with hardening will lead to fracturing. Wich means thickness and slope become irrelevant. The plate will shatter like a plate of grass if the impact is strong enough. Even if not chance is fragments will shower into the vehicles interiour from the point of impact. This effect even has a name because its so common: spalling.
There also is an effect called "overmatch". Wich is very relevant in full caliber AP shells as used during WW2. A plate of armor regardless of slope will be ineffective against a shell wich has a dimaeter bigger than the plates thickness. This is a rule of thumb but it is proven by actual experience. It took years after the war to fully understand why. It is related to the way how full caliber shells work. The distribution of tension around the point of impact and the reflection of shockwaves in the crystal structure of the armor material are important.
What it comes down to is that at the end of the day a thicker plate of armor is a thicker plate of armor. Wich means it offers more protection.
A thinner and sloped plate might duplicate the protection under the right circumstances but this isn't 100 % sure.
A prime example are the British cruiser tanks. These were desigend with sloped armor (especially the turret) to duplicate the effect of a thicker plate and save weight. In theory their armor was quite good. Only it turned out in the field they were paper thin and could be penetrated by any AT weapon.
The T34 was at least proof against 37 mm guns. And offered some protection against 50 mm L42. The 50 mm L60 and all 75 mm (exept for the L24 howitzer) could reliably penetrate it with AP shells. The T34 was only problematic for the Germans when it showed up in huge numbers. Wich it did later in the war. The armor of the KV series and later heavy tanks was problematic.
A thick plate will allways offer the protection that its thickness provides. Even in the worst of circumstances. More often than not it will offer more because a hit is not scored at a perfect angle. With sloped plates its the other way round. It only offers the theoretical protection against a perfect hit.
This combined with the high quality material results in German AFV having better protection compared to AFV with the same armor thickness made by other nations.