Changing the metal in a metalloporphyrin can be a useful way to tune its electronic structure. Nickel porphyrins tend to have larger HOMO-LUMO gaps and lower HOMO levels than zinc porphyrins, resulting in blue shifted absorption spectra and lower chemical reactivity. Using OX-B3LYP, we have calculated NICS(0)zz for c-Ni PN with N = 12, 14, 16, 18 and 20, revealing that the 16-porphyrin ring is the largest nickel porphyrin-based nanobelt to display a global ring current, in contrast to the zinc complexes in which global ring currents persists up to N = 22. (see SI Section E). A related effect is observed in linear l-PN ribbons, in that infinite nickel metallated ribbons are calculated to have a wider band gap than the corresponding zinc ribbons. We now shift our attention to evaluating the strain in these nanobelts. Template-directed synthesis is often used to synthesize porphyrin nanorings, starting conceptually from a porphyrin nanoribbon and then bending it into a ring (Figure ). This process is associated with a considerable increase in strain. We used OX-B3LYP and a hyperhomodesmotic 51 scheme (details in SI Section F), to show that that the total strain in c-PN nanobelts decreases rapidly until about N > 12, then declines more gradually (Figure ) with increasing N. Combining the predicted strain with our NICS calculations, we can identify N = 16-18 nanobelts as the most attractive candidates for synthesis, offering relatively low strain energies and significant ring currents. The belts for N = 6-18 are less strained than cubane, but more strained than cyclopropane, although the strain is spread over a large number of bonds. Aromatic stabilization energy (ASE) is a popular measure of aromaticity, calculated as the difference in energy between an (anti-)aromatic cyclic system and a non-aromatic analogue, which may be linear or cross-conjugated. Classic examples are cyclobutadiene and benzene, which have higher and lower energy, respectively, than their non-aromatic counterparts, corresponding to positive and negative ASE. OX-B3LYP calculations of c-PN nanobelts reveal similar behavior, with even-N belts (with 4n π-electrons) displaying a positive, and odd-N belts (with 4n+2 π-electrons) a negative ASE (Figure ). Here we calculate the ASE as the difference in energy between a particular c-PN and the smooth curve without the oscillation between aromatic and anti-aromatic species, thus avoiding the common problem of defining a non-aromatic reference system. The energetic (ASE-based) criterion of aromaticity is more conservative than the magnetic (NICS-based) one, as the magnitude of ASE drops below 1 kJ/mol at N = 18 (Figure ), while a significant ring current persists up to at least N = 22 (Figure ). The computed ASE values also appear to be less sensitive than NICS to the employed DFA (see Figure ). Recognizing the importance of balancing the description of localization and delocalization in conjugated systems, here we used coupled clusters to build OX-B3LYP, a DFA specifically tuned for the description of edge-fused porphyrin nanobelts. OX-B3LYP predicts the presence of global ring currents in neutral c-PN belts with up to 22 porphyrin units, indicating global (anti-)aromaticity in molecular rings with a Hückel circuit of 220 π electrons and a circumference C = 18.6 nm. This finding considerably pushes the size limit of global aromaticity, as to our knowledge the largest molecules displaying global ring currents in their neutral state reported until now had 54 (aromatic, C ≈ 5.0 nm) 54 and 36 (anti-aromatic; C ≈ 2.5 nm) 55 π electrons. c-PN belts are appealing components for molecular electronics, and they might be particularly suitable for devices which benefit from a large ring circumference, such as Aharonov-Bohm interferometers. The size limit of aromaticity may be pushed even further if charged systems are considered. For example, the butadiynelinked 12-porphyrin ring c-P12-b12 (C = 16.1 nm) displays a ring current in the charged (e.g. 6+) states, but not in the neutral molecule. Indeed, an OX-B3LYP calculation for c-P24 12+ (C = 20.3 nm) yields NICS(0)zz = 25.6 ppm (using a geometry optimized at GFN2-xTB 57 ), indicating a 10-fold increase of the ring current upon charging.