Sometimes it is helpful to see an item you have interest in comparison to a familiar item in order to be able to determine the size before you purchase.  Here are some examples:

1oz |30ml amber glass bottle

2oz |60ml amber plastic bottle

4oz |120ml amber plastic bottle

1oz | 30g clear glass jar

1oz | 30g white plastic jar

2oz | 60g amber plastic jar

INHALER glass amber vial

.33oz | 10ml clear glass ROLLER

 1dram | 3.7ml amber glass dropper

1oz | 30ml clear airless pump

1.7oz | 50ml clear airless pump

4.5oz | 128g white plastic malibu bottle

1oz | 30ml white flip top plastic bottle