Katana have a slight curve and are between about 60-75cm in length (or 24-30 inches).
All the single swords can be neatly classified as uchigatana or tachi. The fomer are essentially long katana, coming in at closer to 90cm (or 36 inches). Tachi are of comparable length, but have a deeper curve situated in the middle of the blade or towards its base. This is thought to be due to their origins as a cavalry sword, whereas the relatively straight uchigatana keeps the point more closely aligned with the wrist for thrusts. Katana, while shorter, follow the essential design philosophy of the uchigatana for comparable reasons. Uchigatana and tachi both predate katana; the latter became preferable due to their interactions with other weapon options and heavy armours. More specifically, heavier armours cause combat to draw closer, so a shorter blade is preferable for finding gaps and weaknesses in armour while being easier to draw — and therefore, to transition to when discarding a longer weapon, such as a spear. This probably plays a role in the prominence of iaijutsu, or the art of drawing strikes and defenses. Following the Sengoku Jidai period, the same iaijutsu principles would remain relevant for the purposes of self defense, but also the peacetime conflicts between individual samurai, ronin, and other classes of warrior.
Note also that a shorter blade is more easily wielded with a single hand. While katana are generally best used with both, this allows them to efficiently accommodate an off-hand weapon or the use of grappling, throwing techniques with an empty hand — once again factoring into a certain anti-armour quality, as grapples are a universal answer to armour. Ultimately, such factors probably have more to do with the effectiveness of the katana as a weapon than factors like quality of steel; a clever design is clever irrespective of the quality of materials, which might be debatable in any case. It might be said that the katana's strength is a matter of its design quality in context of the needs of a warrior or traveler rather than its inherent superiority as a sword — after all, various sword designs from a variety of cultures have their own excellent virtues. Western longswords and bastard swords excel at versatility and the conjunction of offense and defense; many Arab and Indian swords are remarkably effective in partnership with a shield or especially buckler for very close combat actions; Chinese jian have brilliant control of the point without sacrificing as much in cutting compared to the likes of a Western rapier.
This has been Sword Facts. Would you like to know more?