Rotary mowers are powered by an internal combustion engine (i.e. petrol). Such engines can be either two-stroke or four-stroke cycle engines. Internal combustion engines used with lawn mowers normally have only one cylinder. Power generally ranges from two to seven horsepower. The engines are usually carbureted and require a manual pull crank to start them, although an electric start is becoming a sales feature in some countries.

Rotary mowers powered by electric motors are increasingly popular. Usually, these mowers are moved by manual motive power the on-board engine or motor only spins the blades. These have the disadvantage of requiring a trailing power cord that limits its range and so these are only useful for relatively small lawns, close to a power socket.

There is a hazard with these machines of mowing over the power cable, which stops the mower and may put users at risk of electrocution. Installing a residual-current device on the outlet can reduce the risk of electrocution. Cordless electric lawn mowers are also available for small lawns. Electric rotary mowers weigh 45-50 pounds.

Rotary mowers typically have an opening in the side or rear of the housing where the cut grass is expelled. Some have a grass catcher attachment at the opening to bag the grass clippings. The blade is designed to keep the clippings circulating underneath the mower until the clippings are chopped quite small. Other designs have twin blades to mulch the clippings to small pieces.

A "dead man's" switch is required in some places so that the operator must hold a switch to keep the engine running. Typically, this is an extra bar that is held against the handle. Should the operator lose control of the mower releasing the handle, this will cut the power and the blade will be disconnected by disengaging the clutch.

Hover mowers

Hover mowers are powered rotary push mowers that use a turbine above the spinning blades to drive air downwards, thereby creating an air cushion that lifts the mower off the ground like a hovercraft. The operator can then easily move the mower as it floats over the grass.

Hover mowers are necessarily light in order to achieve the air cushion and typically have plastic bodies with an electric motor, although small petrol engines have been used. A different style of movement is often employed with hover mowers whereby operators swing the mower in an arc around themselves because there are no wheels touching the ground to impede movement in sideways directions.

Hover mowers can also be applied to very long grass, since their lightness permits most operators to lift the mower up and then let it sink slowly down while the blades progressively chop up the vegetation. The lifting action is made easier when the mower is moved around with the handle, whilst being held against the operator's mid-body to provide leverage.