The paper investigates the size-dependent optical properties of colloidal PbS quantum dots (Qdots). The authors determine the concentration of Qdots in suspensions using Beer's law, based on the molar extinction coefficient (ε) at high energies. They find that ε scales with the Qdot volume, indicating no influence from quantum confinement in this spectral range. This allows for accurate concentration determination. Around the band gap, ε scales with the cube root of the particle size, similar to PbSe Qdots. The oscillator strength (f0) at the band gap is calculated from ε and scales linearly with the particle size, agreeing with theoretical tight-binding calculations. The exciton lifetime (τ) is also calculated and ranges from 1 to 3 μs, consistent with literature data. The study provides a comprehensive framework for understanding and quantifying the optical properties of colloidal PbS Qdots, highlighting the importance of local field factors and dielectric confinement.The paper investigates the size-dependent optical properties of colloidal PbS quantum dots (Qdots). The authors determine the concentration of Qdots in suspensions using Beer's law, based on the molar extinction coefficient (ε) at high energies. They find that ε scales with the Qdot volume, indicating no influence from quantum confinement in this spectral range. This allows for accurate concentration determination. Around the band gap, ε scales with the cube root of the particle size, similar to PbSe Qdots. The oscillator strength (f0) at the band gap is calculated from ε and scales linearly with the particle size, agreeing with theoretical tight-binding calculations. The exciton lifetime (τ) is also calculated and ranges from 1 to 3 μs, consistent with literature data. The study provides a comprehensive framework for understanding and quantifying the optical properties of colloidal PbS Qdots, highlighting the importance of local field factors and dielectric confinement.