It is best to check the oil in your lawnmower before each use.
Park your lawnmower on a level flat surface and allow it to sit for a few minutes to let the oil settle.
Find your mower’s oil cap. Unlike your car, where the oil cap and dipstick are in separate places on the engine, your mower’s oil cap and dipstick are together. Make sure to look for the oil symbol and do not mistake it for the gas symbol. Most mowers will either say oil or have the oil symbol on the oil cap. It should be on the top or near the top of the engine.
Unscrew the oil cap and pull out the dipstick. Wipe the dipstick off with a clean cloth and insert it back into the oil tank. Screw the cap back on. Unscrew the cap again and pull the dipstick out. Look at the level of the oil on the dipstick. The level should be between the full and add marks. Depending on the brand of mower you have, the marks may look different. There may only be two holes to indicate full and add. You want the level to be between the two holes. As close to the full side as possible without going over.
If you do overfill the oil, your engine will smoke and it can cause damage. It should take around ½ quart to fill the oil. If your oil is just a little low, add oil in small increments until it reaches the full level.
Check your owner’s manual to find out what kind of oil your mower takes. If you no longer have the manual, you can look it up on the manufacturer’s website.