Get an empty measuring cup. Get another container with an opening with a smaller circumference, fill it completely with water and hold it above the cup. Place a strawberry inside the container - the water that empties into the cup will be equal to its volume. Set that strawberry aside - it has been measured. Refill the container. Dunk the second strawberry, etc. Repeat until the cup is full of water. You will have measured out an exact cup of strawberries (i.e. 238 mL).
Get an empty measuring cup. Get another container with an opening with a smaller circumference, fill it completely with water and hold it above the cup. Place a strawberry inside the container - the water that empties into the cup will be equal to its volume. Set that strawberry aside - it has been measured. Refill the container. Dunk the second strawberry, etc. Repeat until the cup is full of water. You will have measured out an exact cup of strawberries (i.e. 238 mL).