Quantum science tools have been pivotal in various precision experiments, such as gravitational wave detectors, atomic clocks, and searches for new fundamental physics and axion dark matter. In experiments with ensembles of spin qubits, the standard quantum limit on sensitivity scales with the inverse square root of the number of spins. Platforms such as cold atoms, atomic vapor cells, and color centers in solids can operate in the regime where this spin projection noise dominates detection of ensemble dynamics. Increasing ensemble size is a promising way to enhance sensitivity. The challenge is that this requires a corresponding reduction in other noise sources. I will present precision nuclear magnetic resonance measurements on macroscopic ensembles of 10^{21} nuclear spins, with sensitivity limited by the quantum spin projection noise. Additionally, I will discuss the creation and utilization of spin squeezing in such macroscopic spin ensembles.