"That's all it would take" is another way of saying "that is all that is required/necessary". For example: "One missed day of work; that's all it would take for you to lose your job." It can also be used as another way of saying "that is the only thing it would accept". For example: "I bought some food from the vending machine, but I had to use quarters. That's all it would take."

The expression "That's all it would take" is commonly used when given instructions for something, but also has other uses. For example: "That's all it would take to change her mind." Instructions: "Takes C batteries. That's all it would take." "Take this medicine. That's all it would take for the sickness to go away." It depends on the way you are planning to use the phrase, really. Also, it means (In examples 1 and 3) "That's all you have to do." Or, like in my second example, "It's the only thing you can do. Like, only option"