Boondocking Days Calculator
Find out how many days your fresh, gray and black tanks allow when you camp without hookups.
Find out how many days your fresh, gray and black tanks allow when you camp without hookups. Free, private, and it shows its working.
How to use this tool
Enter your three tank sizes, how many people are aboard and how much water each person uses per day. The calculator works out when each tank fills or runs dry and shows which one limits your stay.
Daily use varies a lot between households, so track your real use for a few days and update the numbers. Plan to dump or refill before the calculated limit, because tank gauges are often inaccurate.
Worked example
Here is what the Boondocking Days Calculator returns with its starting values. Replace them with your own numbers for a real plan.
| Input | Example value |
|---|---|
| Fresh water tank | 40 gal |
| Gray tank | 35 gal |
| Black tank | 30 gal |
| People on board | 2 people |
| Fresh water per person per day | 3 gal |
| Share of fresh water that ends up in gray | 80 % |
| Black tank use per person per day | 1.5 gal |
| Result | Value |
|---|---|
| Days before a limit | 6.7 days |
| Limiting factor | fresh water |
| Fresh water lasts | 6.7 days |
| Gray tank fills in | 7.3 days |
| Black tank fills in | 10 days |
How the calculation works
- Fresh use per day = 2 people x 3 gal = 6 gal.
- Gray inflow per day = 6 gal x 80% = 4.8 gal.
- Black inflow per day = 2 people x 1.5 gal = 3 gal.
- Days = tank size / daily use for each tank; the smallest number is your limit.
When this tool helps most
Use it before a boondocking trip to choose how long to stay and where to dump and refill on the way.
Common mistakes to avoid
- Trusting tank gauges that read full or empty incorrectly.
- Forgetting that dishwashing and showers drive gray tank use.
- Planning a stay right up to the limit with no margin.
Related guides
This tool is for planning and education only. It does not store your entries. Read our disclaimer.
Understanding your results
- Limiting factor: fresh water, gray tank, black tank or power, whichever runs out first.
- Days off-grid: how long you can stay before refilling or dumping.
- What to change: the habit or upgrade that extends your stay the most.
Two quick scenarios
Gray tank fills first
Many RVers run out of gray tank space before fresh water, so shorter showers and dishwashing in a basin help.
Power limits the stay
If power runs out first, more solar or a larger battery extends the stay more than bigger tanks.
Before you rely on the numbers
- Check stay limits on public land.
- Know where the nearest dump station is.
- Carry extra water containers if allowed.
- Pack out all trash.
Keep planning with Free camping in the US and RV Solar Sizing Calculator.
Official references
Frequently asked questions
It depends on tank sizes, people aboard and your habits. The calculator divides each tank by your daily use and shows the smallest result, which is your limit. Often fresh water or the gray tank, because showers and dishes use the most water. Enter your own numbers to see which applies to you.How long can I boondock with my RV tanks?
Which tank usually runs out first?