Model pores, hosts, and solvated cavities with confidence. Choose shape, enter dimensions, get effective diameter. Download clean reports for lab notes and sharing today.
| Scenario | Inputs | Key output |
|---|---|---|
| Sphere cavity | Radius = 0.50 nm | Volume ≈ 0.524 nm³, diameter = 1.00 nm |
| Cylindrical channel | Radius = 0.40 nm, height = 1.20 nm | Volume ≈ 0.603 nm³, eq. diameter ≈ 1.04 nm |
| Ellipsoidal host pocket | a=0.60 nm, b=0.45 nm, c=0.35 nm | Volume ≈ 0.396 nm³, eq. diameter ≈ 0.91 nm |
| Crystal void method | Unit cell = 25000 ų, void = 48%, cavities = 2 | Per cavity ≈ 6000 ų, eq. diameter ≈ 2.24 nm |
Cavity volume links structure to function in inclusion complexes, adsorption, and solvated pockets. A spherical cavity with 0.50 nm radius has about 0.524 nm³ volume, matching 524 ų, while its equivalent diameter is 1.00 nm. These numbers help anticipate selectivity, diffusion limits, and whether a guest fits without severe steric strain. Reporting both ų and nm³ improves comparability across crystallography and simulation datasets. To gauge transport, compare cavity diameter with Stokes diameter, allowing 0.1–0.2 nm clearance to represent thermal motion, solvation, and flexibility during diffusion in liquids.
Choose the simplest shape that preserves the dominant constraint. Cylinders are useful for channels; with r=0.40 nm and h=1.20 nm, volume is near 0.603 nm³. Ellipsoids capture anisotropy; using a=0.60, b=0.45, c=0.35 nm yields roughly 0.396 nm³. Boxes can approximate voids in frameworks when orthogonal dimensions are known. Consistent units prevent scaling errors during conversion.
Different shapes can share the same volume, so an equivalent-sphere diameter offers a common language. The calculator converts V to d = 2·((3V)/(4π))^(1/3). Diameters below 2 nm classify as micropores, 2–50 nm as mesopores, and above 50 nm as macropores. Pair diameter with surface area, because higher area at fixed volume often indicates stronger host–guest contact potential and higher sorption capacity.
When unit-cell void data are available, compute accessible void volume as Vcell·(void%)·(accessible%). If Vcell is 25000 ų and void is 48%, accessible void is 12000 ų at 100% accessibility. Dividing by two cavities per cell gives 6000 ų per cavity, corresponding to an equivalent diameter near 2.24 nm. This approach is fast for screening porous solids and comparing batches.
Guest counts are approximate because real molecules are not perfect spheres. The tool models guests as spheres and applies a packing factor p and occupancy o: N ≈ floor(p·o·Vcavity/Vguest). Random packing around 0.64 is conservative, close packing near 0.74 is optimistic, and simple cubic near 0.52 is restrictive. Use occupancy below 100% for blocked entrances or strong binding that reduces free volume.
Choose a length unit for geometry inputs. The tool converts to meters internally, then reports volume in ų, nm³, and cm³. For void fraction, enter unit-cell volume in ų or nm³ for consistent results.
Use a sphere for roughly isotropic pockets, a cylinder for channels, an ellipsoid for elongated cavities, and a box for orthogonal voids. If unsure, start with a sphere, then compare sensitivity across shapes.
It is the diameter of a sphere that has the same volume as your selected shape. This normalizes different geometries into one comparable size metric, useful for pore classification and quick screening.
It multiplies unit-cell volume by void% and accessible% to get accessible void volume, then divides by cavities per cell. The resulting per-cavity volume is converted to an equivalent diameter and surface area for reporting.
Packing approximates how efficiently spherical guests fill space. Random packing is ~0.64, close packing is ~0.74, and simple cubic is ~0.52. Multiply by occupancy to account for blocked entrances or strong binding.
Real cavities are irregular, flexible, and partially solvated, while guests are not perfect spheres. Experimental pore sizes can include connectivity and probe effects. Treat outputs as screening values, then refine with structure models or simulations.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.