How capacitive is the human body?

Testing a capacitive screen, it's clear that it can tell the difference between a celery touching it (human holding it with an isolating material) and a human touching it. Touching it holding a celery, but no isolating material works too.

So, what is the range of 'normal' capacitive potential of a human body?

(I am not interested in capacitive screens, but rather on electrical properties of human bodies, however, the capacitive screen got me interesting on it).

How could we measure it?

There is no such thing as inherent capacitance of a object. Capacitance is a property between two conductors. Your question therefore makes no sense. Capacitance of a typical human to where?

In the case of touch screens, the sensors are measuring capacitance back to their own ground. How well a human touching a sensor couples back to that ground has a lot to do with the surrounding physical layout. Capacitive touch sensors typically work on sensing a change of a few pF, sometimes even less than 1 pF, over a few 10s of ms.

In reading this over I think I left the wrong impression on how capacitive touch sensors really work. Actually, they only measure the change in capacitance as a conductive object such as your finger is put in close proximity to the sensor. Such a sensor has two plates, sometimes interleaved, so that putting your finger close increases the capacitance between the plates.

This doesn't change the fact that the human body will have some capacitance to the local ground, which is more what this question is about. Again though, there is no fixed inherent capacitance of a human body by itself.

• Then a human + a touch screen be a kind of capacitor? (which can be measured). The capacitance would increase, as the two 'plates' of this capacitor approach and that's what a touchscreen registers as a touch. – Quora Feans Oct 8 '13 at 14:03
• It is not true that capacitance requires two bodies. Most E&M text do problems where a lone conducting sphere is treated as a capacitor. You just measure the potential against zero at infinite remove (the usual Coulomb gauge) and away you go, still defining $C = q/V$. – dmckee Oct 23 '13 at 3:02
• @dmcke: But none of that is relevant or useful for capacitive touch screen sensors. In any practical sense in a electronic circuit, capacitance is always between two nodes. – Olin Lathrop Oct 23 '13 at 12:18
• I don't agree with the attitude of this answer. An industrial capacitor has an inherent capacitance, or at least the specified expected value of a capacitance. You know the intention of the question, but your answer is simply getting ahead of yourself. The human body of a 200 lb adult is about 250 pF. – Cynthia Avishegnath Jan 15 '17 at 5:01
• @Cynthia: Industrial capacitors can specify a fixed capacitance value because the entire capacitor is contained in the device. It has two leads connected to the two plates. A human body is just one connection, which makes one plate of a capacitor. The capacitance to some other plate depends on the size, distance, and shape of that other plate. – Olin Lathrop Jan 15 '17 at 14:18

If we assume a perfectly spherical and conductive human body, we need approximately 30 pC to raise the voltage by 1 V, that would be 30 pF.

Only, as Olin pointed out, this quantity is not what is called the capacitance of a conductor, which, for historical or practical reasons, is defined for a pair of conductors.

• Spherically filled ... – bmargulies Feb 3 '15 at 2:31