Question

What is the difference between NTP and STP?

Answer 1

Let us know about STP first. Standard temperature and pressure (STP) are conditions that must be established for experimental measurements in order to make comparisons between different sets of data. The International Union of Pure and Applied Chemistry (IUPAC) and the National Institute of Standards and Technology (NIST) are the most widely used standards, albeit they are not generally approved. For their standard reference circumstances, other organisations have produced a range of alternative definitions.

Complete answer:

Standard temperature and pressure	Normal temperature and pressure
IUPAC (International Union of Pure and Applied Chemistry) defines STP (Standard Temperature and Pressure) as air or gas at $0^\circ C{\text{ }}\left( {273.15{\text{ }}K,{\text{ }}32{\text{ }}^\circ F} \right)$ and $105{\text{ }}pascals{\text{ }}\left( {1{\text{ }}bar} \right)$	Air or gas at $20^\circ C{\text{ }}(293.15{\text{ }}K,{\text{ }}68^\circ F$) and $1$atm ($101.325{\text{ }}kN/m2,{\text{ }}101.325{\text{ }}kPa$) is described as NTP (Normal Temperature and Pressure).
STP is defined as air at $60^\circ F{\text{ }}\left( {520^\circ R,{\text{ }}15.6^\circ C} \right)$ and $14.696$ psia in the Imperial and US systems of measurement ($1$ atm, $1.01325$ bar)	NTP is frequently used as a standard condition for fan capacity testing and documentation.
A mol of gas has a volume of $23.6442$ litres at these conditions.	A mol of gas has a volume of $22.4136$ litres at these conditions.

Note:
Standard reference conditions for expressing the volumes of gases and liquids, as well as related quantities such as the rate of volumetric flow (the volumes of gases vary significantly with temperature and pressure) are often required in industry and commerce: standard cubic metres per second $\left( {S{m^3}{s^{ - 1}}} \right),$ and normal cubic metres per second $\left( {N{m^3}{s^{ - 1}}} \right).$