Efficient: eficiente vs. eficaz

Question

The English "efficient" can be translated as either eficiente or eficaz in Spanish. What is the difference between these two translations? In what situations can each be used?

Answer 1

I think many people would use them interchangeably, but they are not exactly the same. Both are defined as "que tienen eficacia" (eficaz) and "que tiene eficiencia" (eficiente). Now, let's look at the meanings of eficiencia and eficacia:

eficiencia.
(Del lat. efficientĭa).
1. f. Capacidad de disponer de alguien o de algo para conseguir un efecto determinado.

eficacia.
(Del lat. efficacĭa).
1. f. Capacidad de lograr el efecto que se desea o se espera.

So, they're similar but not really the same.

I, being an engineer, understand eficiente as "producing the desired effect with the least resources possible" and eficaz just as "producing the desired effect".

If you look up efficient in the Webster dictionary, the second definition is:

2: productive of desired effects; especially : productive without waste (an efficient worker)

And there's another word, effective, which is defined as:

1 a : producing a decided, decisive, or desired effect (an effective policy)

So I would say:

Eficiente: efficient (as in productive without waste)

Eficaz: effective