Crack control: why codes limit bar spacing, not just strength
A section can have plenty of reinforcement by area and still crack more than a code will allow — because crack width is controlled by how that steel is spread out, not just by how much of it there is.
Reinforced concrete is expected to crack under service loads — that's normal, not a defect, since concrete's tensile capacity is far lower than the loads reinforcement is designed to carry. What codes actually control is crack width, not whether cracking happens at all, because a few genuinely wide cracks are a real problem in a way that many fine, hairline cracks are not: wide cracks let in moisture, carbon dioxide and chlorides that corrode the reinforcement over time, and they're also simply unsightly and can make a structure feel unsafe even when it isn't.
Why spacing controls crack width more directly than area
This is where reinforcement quantity and reinforcement distribution genuinely diverge as two different questions. A section could technically satisfy its required steel area with a few widely-spaced, large-diameter bars — but wide spacing means that between any two bars, the concrete has a long unsupported stretch where it can build up tensile stress on its own before a bar is close enough to intervene, and when that concrete eventually cracks, the crack tends to open wider before the reinforcement really engages. Using more, smaller-diameter bars spaced more closely gives the same total steel area, but spreads out where and how often the concrete gets "picked up" by a bar — which produces more numerous, individually narrower cracks instead of fewer wide ones.
This is exactly why EC2 and ACI 318 both include maximum bar spacing provisions specifically aimed at crack control, layered on top of (and separate from) the minimum reinforcement area required for strength — satisfying one doesn't automatically satisfy the other. It's also a genuinely different limit state: this is a serviceability check, about how the structure performs and looks under everyday loads, not an ultimate-strength check about whether it can carry its factored design loads at all. RC Beam Design and RC Slab Design both carry the bar layout you choose through to this kind of check, not just the total reinforcement area (see the related tools below).