I was wondering, how can both a proton and a neutron weight 1u? An Up quark has a mass of 1.7–3.1 MeV (according to Wikipedia). Down has a mass of 4.1-5.7 MeV. Average Up: 2.4 Average Down: 4.9 If a proton is Up+Up+Down (2.4+2.4+4.9) it has a mass of 9.7 MeV. A neutron is Down+Down+Up (4.9+4.9+2.4), and it has a mass of 12.2 MeV. How can protons and neutrons have the same mass? Sorry if it's kind of confusing.