From a Westinghouse Catalogue, probably from the '50s.
A DC relay similar to the one illustrated would be around 18.5 lbs, with dimensions about 9"x8"x9". Smaller versions existed (with fewer contacts), and these could be down to about 9lb
An AC (vane) relay is much heavier. A typical example, the H2, was 29lb with dimensions about 10"x9"x10.5". With a detachable top, this went up to 38lb with dimensions 10"x9"x12".
The early large type plug-in relays (bigger than the BR design) were smaller, and lighter than a DC relay. A typical DC one weighed 11lb, and measured 3.25"x9.75"x8.5". An AC vane one weighed 16lb and measured 6.5"x9.75"x8.5".
One thing to note, the move to plug-in relays was a conscious trade-off between size and efficiency. One reason the shelf type relays were so large and heavy was that the magnetic circuit was designed to be efficient and use little power to hold up. By the fifties, power supplies had improved (particularly for the large relay schemes coming into use) and so a higher power consumption could be tolerated, but large relays couldn't be.
You can do the conversion into metric yourself, 1lb is 0.45kg or 9lb is roughly 4kg. No wonder I sweated a bit carrying an AC Vane relay with top home from Spotswood
Of course even older relays are even larger and heavier. Try a polyphase relay!