Honestly, there isn’t one universal number because “standard” depends on the material and frame style. In my experience, a typical 6-foot steel urban bench with timber or recycled slats lands between 120 and 250 lb (about 55–115 kg). Cast iron or concrete models can easily run 250–400 lb or more, while lightweight aluminum or recycled plastic benches may be as low as 60–100 lb.
Can one person move one easily? For most full-size steel or cast iron benches, no—not safely as a dead lift. The weight itself is part of it, but the real problem is the shape: benches are long, unbalanced, and have no good handholds. A lighter 60–90 lb aluminum bench can be dragged or walked short distances by one fit person, but even then it is awkward.
If you need to relocate a standard bench, I’d treat it as a two-person job. Two people can usually lift and carry a 150–200 lb bench for a short distance if they use proper lifting technique and lift from the ends or frame, not the slats. For anything over about 200 lb, or for concrete benches, use a heavy-duty hand truck, furniture dolly, or moving straps—and remove the bench from its anchor bolts first. On soft ground or slopes, get a third person or mechanical help.
So my practical rule is: under about 80–100 lb and compact, one person might manage with a dolly; standard commercial benches over 120 lb should be moved by two people, and anything cast iron or concrete should be moved by a team or with equipment. If you are not sure, assume it is a team lift.