In your example you have a 30kg limit, which would allow you to check a single bag weighing 30kg, OR one bag weighting 10kg and another weighing 20kg, OR three bags weighting 10kg each. With a weight model, excess baggage charges generally only apply if your total weight is over the allowed weight.
The 30k generally means that you are allowed to check in up to 30 kilograms of luggage (sometimes it can be measured in pounds) on the flight, depending on the fare class and route. This weight limit applies to both checked baggage and any carry-on baggage you may bring with you.
Small to medium-sized suitcasesThese suitcases are perfect for short business trips or that city trip to Rome you've been thinking about. The suitcases have capacities of about 25 to 50 liters, which equals about 10kg of luggage.
2 pieces of free checked baggage with a maximum weight of 30kg/66lbs combined. 1 free carry-on bag weighing a maximum of 7kg/16lbs. 30kg/66lbs of free checked baggage (maximum 2 pieces) on most flights.
Although there are various shapes and sizes, most 23 kg suitcases have large and extra large suitcase dimensions and are appropriate for checked-in travel on airlines. Typically, a 23kg suitcase size will have the following measurements: Length: 71-81 cm (28-32 inches )
If you've booked a flight only, then you'll have 10kg of hand luggage included. The maximum size of this should be 55x40x20cm. You can also pay to add checked-in luggage, weighing either 20kg or 25kg, depending on your booking.
50-75 liters: For a trip that lasts one to two weeks, many people jump up to a bag in this range. 75 liters-100+ liters: For big expeditions, travelers typically need several large bags that can hold 75 liters or more each.
Emirates Checked Baggage Allowance:The weight can be distributed across as many bags as you like. Items must not exceed 300 cm (118 in) in total dimensions. No single bag may weigh more than 32 kg (70 lbs). On flights within the Americas and within the US and Europe, allowances are based on a 'piece concept'.
Carry-on bags are limited to 22 inches long, 14 inches wide and 9 inches high including wheels and handles. All three measurements shouldn't add up to more than 45 inches.