Use this chemistry calculator to reproduce a named relationship with explicit quantities and units for study, laboratory planning, or an independent numerical check.

IC50 (mol/L)

Required number input.

Km (mol/L)

Required number input.

[S] (mol/L)

Required number input.

Convert IC50 to Ki using Cheng-Prusoff equation Ki = IC50/(1+[S]/Km). The tool evaluates the supplied inputs together and returns the named outputs below; it does not infer omitted operating conditions or change the units shown.^[1]

Ki (mol/L)

The resulting ki returned as a number.

• Compact enzyme-kinetic equations generally assume a defined mechanism, initial-rate conditions, stable enzyme concentration, and negligible substrate depletion. Cooperativity, inhibition type, transport, and assay artifacts can invalidate those assumptions.
• Use finite inputs in the displayed units and preserve more precision than the final presentation requires. Independently verify safety-critical, financial, compliance, or production decisions.

Check units and significant figures, compare the result with limiting cases, and use measured or source-specific constants where available. Laboratory, safety, and regulatory decisions require validated methods and appropriate uncertainty analysis.

• Inhibition Constant Ki Calculator

  Compute Ki from IC50 via Cheng-Prusoff Ki = IC50/(1+S/Km).

• Absorbance From Transmittance

  Convert percent transmittance to absorbance.

• Binding Energy Per Nucleon Calculator

  Convert a mass defect into total binding energy and divide by the nucleon count using 931.494 MeV per atomic mass unit.