My information comes mostly from the Napoleonic Wars, which I would place outside the Early Modern period. While they were all fought with the same weapons as earlier conflicts, there use on the battlefield was often quite different, so applying it to earlier periods should be done carefully. Just in terms of broad figures, the ratio of killed to wounded could vary a great deal; on the low end, one to ten would not be unheard of, while at the other extreme, one in three could also occur, especially under unfavorable circumstances.

One important aspect of casualties in Early Modern warfare is the nature of the wounds in question. When a body of men is engaged more by other infantry armed with muskets, artillery, or cavalry armed with cold steel, they suffer very different types of wounds, and this affects in part the proportion of killed and wounded.

The Spanish Army of Flanders produced excellent medical records from the latter 16th century through the 17th, and offers a wealth of information about Early Modern warfare. There, they rightly considered gunshot wounds by far the most serious, as they could inflict maladies contemporary medicine could not treat: internal bleeding, blood poisoning, and shattered bone meant a wounded soldier who suffered these specific problems would count himself lucky to simply lose the afflicted limb. When amputation was impossible, as in the case of torso wounds, operation was especially hazardous.

As bad as firearms were, artillery was even worse, as an iron cannonball flying at more than a thousand feet per second will obviously smash any living thing in its path; a man would count himself lucky if he was permanently maimed rather than killed outright by heavy guns. Even when roundshot appeared to slow down to roll across the ground, many soldiers would discover the hard way that it still had incredible angular momentum; if they stuck their foot out to stop it rolling, they could find the bones in their foot and shin crushed. Men could be killed by fragments of their comrades' bones flying from their bodies. In one engagement during the Seven Years War, French surgeons despaired of saving even 2% of the 1500 wounded, who had mostly suffered canister wounds.

On the other hand, cuts by swords and pike thrusts were relatively easily treated. Sabre cuts were probably the least serious wounds an Early Modern soldier could receive, except when they struck something vital like the eyes; many soldiers survived several such cuts and experienced quick healing after the bleeding was staunched and the cut sutured closed. Templehoff's history of the Seven Years War records the complaint of one artilleryman who witnessed a cavalry engagement.

You must pardon me if I venture the opinion that the shock of cavalry is not as decisive as it seems to be. In the campaign of 1762 I witnessed a shock [at Reichenbach] which was delivered by the greater part of the Prussian cavalry against a still larger force of Austrian cavalry. It resulted in a few hundred wounded and prisoners on the two sides. Not a single dead man lay on the field of battle.

In general, the different forms of combat individual units were exposed to often affected the ratio of killed to wounded. Every combat is of course unique; some cavalry combats were more deadly than others, while artillery bombardments with shells might produce a great many more wounded than dead, but there is evidence for general trends.