The phrase "a quantity that is" is correct and usable in written English.
It can be used when describing or defining a specific amount or measurement of something in various contexts, such as mathematics, science, or general descriptions.
Example: "In this experiment, we need to measure a quantity that is greater than 50 milliliters to ensure accurate results."
Alternatives: "an amount that is" or "a measure that is".
She has published well over 100 books, including more than 40 novels, lately at the rate of at least one a year, a quantity that is remarkable for the quality control of both her storytelling and her sentences.
Evaluation of the spatial integral leads to a quantity that is now taken to represent the change in kinetic energy of the mass resulting from the action of the force and is just one-half the vis viva.
In setting a tolerance level, the Food and Drug Administration reviews tests of the poison on laboratory animals and then establishes as the maximum level of contamination a quantity that is much less than that required to produce symptoms in the test animals.
Newton's laws of motion and of gravitation and Coulomb's law for the forces between charged particles lead to the idea of energy as a quantity that is conserved in a wide range of phenomena (see below Conservation laws and extremal principles).
For if the velocity of light in empty space is to be a quantity that is independent of the choice (or, respectively, of the state of motion) of the inertial system to which it is referred, no absolute meaning can be assigned to the conception of the simultaneity of events that occur at points separated by a distance in space.
There exists only one kind of resource, with a quantity that is given and known.
Using lambda phage packaging to accomplish size selection instead of the original gel-based method, Williams was able to reduce the input requirement to as little as 3 μg, a quantity that was much easier to procure for these organisms.
The term biomarker is used here in a general sense for any quantity that is linked to drug effect.
For any quantity that is conserved, an inventory rate equation can be written to describe the transformation of the conserved quantity.
The degree of hypoxia is a dynamic quantity that is influenced by physiological factors.
Batch ordering requires orders that are integer multiples of a fixed quantity that is larger than one.
