Both fantasy and historical fiction love knights. And, as everyone knows, knights often mean armor. Plate armor, to be precise. The problem is that some seem to think that plate armor was practically weightless while others have knights flailing helplessly on the ground waiting to be slaughtered should they slip on the mud, because of their armor’s weight. So, just how much does plate armor weigh, anyway?
Thankfully, Eric Lowe has the answer on Quora.
Was Armor Heavy?
Yes, of course it was. There’s a tendency to answer questions like this with a denial. I think people are afraid that if you admit that a man-at-arms’s armor was heavy, people will get the wrong idea, or ask for the millionth time, “But how can you fight in armor that’s heavy?”
However, knightly armor typically weighed around 40 kilos, which makes it comparable to modern infantry kits: A “basic” modern American soldier or Marine carries about 35 kilos, while a study done on Marines in Iraq came out to an average of 60 kilos.
As to how people fought in it, it helps that the armor’s weight was [generally] better distributed across the body than modern infantry kit is. It’s less like carrying an extra 40+ kilos and more like you’ve just suddenly gained a lot of weight.
Also, consider the alternative. Armor was worn because people liked to stay alive. It was supposed to let you take a halberd to the face, turn the blows of a heavy lance driven by a warhorse and another man in armor, and withstand the force of a 180-pound longbow, a 1,000-pound crossbow, or an arquebus.
Now, does this mean you can’t fight in it? Obviously, no. Suppose you did have to go about your business carrying an extra 40+ kilos of body weight. You can adapt to that. There’s no trick to it, just the discipline of suiting up and working in your kit. Regularly force your muscles to move an extra 40+ kilos, and they’ll figure it out. It’s a very straightforward process.
It also helped that people trained in this sort of thing from an early age. Also, if you didn’t do it — well, your chances of survival were pretty slim. So, while armor was too heavy to be considered a second skin, it was possibly similar to a very heavy raincoat in terms of comfort.
Finally, it should be remembered that people didn’t actually have to wear it that often, even while on campaigns. Throughout history, pitched battles were relatively rare in comparison to sieges. And you really don’t need to wear a full suit of plate during a siege unless you’re on the front line during an assault or close to the wall constructing siege equipment/filling in ditches. Most soldiers would be fine with just staying out of range and wearing a breastplate to be safe.
Piece of Cake Then, Right?
Well, no.
The nuance is although modern infantry kit weighed more or less the same (sometimes more), it is usually focused around only the back/upper torso.
Whereas the weight when wearing plate armor is distributed throughout your whole body, including your limbs. When you tire your arms, wrists, and legs like that, you’re going to need to exert more power and energy. More energy consumption equals faster fatigue. Plus, those helmets probably had poor ventilation, so energy consumption would rise even further — one of the reasons why most knights needed a horse.
This is not guesswork, either: a study by the University of Leeds put armor-wearing volunteers on treadmills, as reported on LiveScience. The researchers found that wearing a full suit of armor (which might weigh up to 110 pounds, or 50 kilograms), takes more than twice the energy of walking around unencumbered. Even lugging around a backpack of equal weight is less energy-intensive than wearing armor because wearing 17 pounds (8 kg) of steel plates on each leg requires no small amount of extra exertion.
Note that the helmet was up and the study was conducted in non-combat and constant conditions on a treadmill. This would be exacerbated and way worse in normal terrain, which is usually not smooth.
Eventually, the problem wasn’t the armor’s weight but overheating; if you are fit, you can endure an hour of energy consumption at roughly 10 times the sedentary level. That, however, generates a whopping 1KW of heat, and dissipating that isn’t going to be easy wearing full armor even with the visor up.
To overcome this limitation, weight armor was primarily for use on horseback, or for “ride to near where needed and dismount to walk twenty or thirty yards and engage.”
Finally, a caveat is that armor weight is tricky. There’s tournament armor, jousting armor, armor for fighting mounted, and armor for fighting on foot. Sometimes it was the same set, but configurable, as the image below demonstrates:
So, and depending on the configuration, it may well be that a beer stein tower is actually far heavier than your plate armor. On the other hand, just how rough is that tavern that you need armor to walk in??