<p>Covalent bonding between atoms (molecules) constitutes the rich diversity of nature ranging from the very recently realized one-electron carbon-carbon σ-bond to the well-known hybridized bonds in diamond. This diversity in covalent interactions raises fundamental questions about universal correlations between their electronic structure and mechanical properties. We unveil in this report a general linear correlation of bond strength with the bond order of C–C covalence. From the one-electron σ-bond predicted by Pauling ¹ and vindicated by Shimajiri et al². with a bond strength of 1.49 nN and a bond length of 1.98 Å, all the way to the six-electron σ + 2π bond of 25.72 nN in bond strength 1.20 Å in length, the strength and the order of C–C bonds follow a linear relationship with a slope of 8.9 nN/order. The linearity persists in 13 types of covalent interactions, with prominent examples including Si<b>–</b>Si and B<b>–</b>N covalent bonds. Such a linear scaling law establishes a broad guidance for predictive tuning of covalent bond strengths via bond order engineering.</p>