Blades are measured diagonally from cutting tip to cutting tip.
All of the after market suppliers have a list of blades by length.
Some are on line while others are only in their printed catalogue.
So you start with getting the length right, then look at the size & type of mounting holes then width & finally thickness
The final bit to consider is the shape.
Some blades are flat while others are cranked to protect the mounting bolts .
So a trip to a frelance mower repair shop would be worth your time.
Most will deal with all of the non genuine suppliers and will have all of their catalogues under the counter.
I run into this problem all the time because most of what was imported got rebadged using local brand names