One kilonewton is exactly 1,000 newtons. The prefix does the whole job, but the pair is worth a page because the kilonewton is the working unit of structural engineering and the newton is the one everything else is defined in.
About the units
The newton is defined as the force that gives one kilogram an acceleration of one metre per second squared. It is a small unit in construction terms: the weight of an apple is about one newton, and a person weighs some 700 to 900. Structural loads are therefore expressed in kilonewtons, where a kilonewton is roughly the weight of 102 kilograms. Above that the meganewton appears in bridge and dam engineering. The relationship between force and mass under gravity is the one to keep straight: a mass of 1,000 kg exerts a force of 9.807 kN, not 1 kN.
The exact factor
The factor is exactly 1,000. The conversions that matter in structural work are the ones to mass: 1 kN is 101.97 kgf, so a load of 10 kN corresponds to about 1.02 tonnes resting under gravity. Engineers often use the approximation that a tonne is 10 kN, which is high by two per cent and standard practice in preliminary sizing. Distributed loads are given in kilonewtons per square metre — a typical office floor is designed for 2.5 to 3 kN/m², which is about 250 to 300 kilograms per square metre.
Where you meet this conversion
Structural engineering throughout: beam reactions, column loads, foundation pressures and wind loading are all in kilonewtons. Climbing and rigging equipment is rated in kilonewtons, and the numbers are worth understanding — a climbing carabiner rated 24 kN holds about 2.4 tonnes along its major axis. Crane capacities, lifting slings and anchor points use the same unit. Materials testing machines report in kilonewtons while the resulting stresses are computed in megapascals.