In the car's segment, this one provides excellent legroom and headroom. 4 adults can sit comfortably or else 5 medium build adults can sit with some minor adjustments.
The payload for Maruti Suzuki Celerio is 330 to 435 kg whereas for Wagon R it is 400- 500 kg. So, the weight carrying capacity is not more than Wagon R.
For calculating the load-carrying capacity you need to consider two factors, i.e. the curb weight and the GVM.
The curb weight is the total mass of a vehicle with standard equipment and all necessary operating consumables such as motor oil, transmission oil, coolant, air conditioning refrigerant, and sometimes a full tank of fuel, while not loaded with either passengers or cargo.
The GVM is the gross vehicle mass (GVM) is the maximum operating weight/mass of a vehicle as specified by the manufacturer including the vehicle's chassis, body, engine, engine fluids, fuel, accessories, driver, passengers, and cargo but excluding that of any trailers.
To calculate the load-carrying capacity of a car all you need to do is subtract the curb weight from the GVM. This gives you the payload capacity of the car i.e. is the load-carrying capacity of the car.
Hope this answers your doubts.