How big a tank do I actually need?

Specialist-community consensus is that 1-gallon hand-pump sprayers suit spot-treating and small beds, 2-gallon units handle modest yards, and 4-gallon backpacks are the sweet spot for half-acre-and-up properties. Reviewers caution that a full 4-gallon backpack can weigh roughly 40 pounds, so capacity is a trade-off against carry comfort.