The slowest pot does not set the schedule
Three reservoirs on one round get refilled on one interval, and that interval belongs to whichever one empties first. At the defaults here the office corner holds 40 fluid ounces and uses 8 a day, so with 90 percent of it reachable it lasts 4.5 days. The kitchen shelf lasts 6.2 and the bedroom window 6.5.
Refill on the average and you are working to 5.3 days, which is 0.8 of a day too late for the office corner every time. The average is a number about the group; the schedule is a fact about the worst member of it. This is the same structure as the tanks in a camper, where the trip ends when the first one fills or empties regardless of how much room is left in the other two.
Not all of a reservoir is reachable
Below the foot of the wick, or below the inlet on a sub-irrigated planter, there is water that will never move. It counts toward the capacity printed on the box and toward nothing else. The reachable share field is where that goes, and 90 percent is a placeholder rather than a figure to trust.
Measuring it is a one-off. Run one reservoir until it stops drawing, then tip out what is left and measure it. At the defaults, the 10 percent that cannot be reached across all three is 8 fluid ounces permanently parked below the working level.
What a measured rate is worth
The single most valuable input on this page cannot be looked up. Fill every reservoir to a mark, wait a week, and measure what each takes to get back to the mark. That is the span mode, and one week of it beats any general figure, because use rate depends on the pot, the plant, the room, the season and the light, all at once.
It also has a shelf life. A rate measured in February is not the rate that applies in July, and a rate measured with the blinds open is not the rate with them shut. The allowance field exists so you can apply your own correction rather than pretending the measurement is permanent — set it to 130 and every row is worked at 30 percent above what you measured.
Sizing for a stretch away
Working backwards from a number of days is the useful direction. At the defaults, ten days at the measured rates needs 35 fluid ounces reachable in the kitchen, 80 in the office and 22 in the bedroom. Only 21.6, 36 and 14.4 are available, so all three fall short, and the page reports the capacity each would need: about 38.9, 88.9 and 24.4 fluid ounces respectively, once the reachable share is accounted for.
The office corner is the interesting one, because it needs a reservoir more than twice the size it has. That is a purchase or a rearrangement, not an adjustment, and knowing it before booking is more useful than discovering it afterwards.
What this page is not
It is a volume-over-time calculation. It does not know whether a plant tolerates a dry reservoir, whether wicking keeps up with the rate you measured, or whether any of this is a good idea for a particular species. Those questions belong to a supplier, a local extension service, or your own records.
Two things worth naming plainly. A reservoir is standing water indoors by design, and standing water grows organisms — unremarkable for most households, worth a conversation with a doctor for anyone whose immune system is compromised. And a full reservoir is weight: 40 fluid ounces is about 2.6 pounds of water sitting on whatever the pot sits on, before the pot, mix and plant are counted.
Questions people ask
Can I use this for one pot?
Yes. Fill in a single row and leave the other two blank, and the page reports the days that one reservoir lasts, whether it covers the stretch you entered, and what capacity would. The comparison sections that talk about which one empties first are skipped when there is only one, because there is nothing to compare it against. The refill-round arithmetic is also skipped for the same reason.
How do I measure how much a reservoir actually uses?
Fill each one to a mark you can see or feel, note the date, and leave them alone for about a week. Then measure the water it takes to bring each back to the same mark, using a jug rather than a guess. Switch the rate mode to the span option, enter the number of days and the total each took, and the page divides. A week is long enough to average out a hot day and short enough that the season has not moved underneath you.
What does the reachable share actually mean?
It is the fraction of the stated capacity that the wick or the inlet can lift. Water below the point where the wick reaches, or below the level the pot draws from, sits in the bottom permanently and inflates the capacity figure without extending the interval by a single hour. Running one reservoir until it stops drawing and measuring what pours out afterwards gives you the number for your own pots, which is worth doing once because it is applied to every calculation here.
Why does the page ask for a rate change while I am away?
Because the rate you measured applies to the conditions you measured it in, and a stretch away is usually a different set of conditions: heating left on or turned off, blinds closed, a different month. The field takes your own allowance as a percentage of the measured rate and applies it to every row, so 130 works everything at 30 percent above measured. It defaults to 100, meaning no change, which is convenient rather than realistic.
Does this tell me whether my plants will survive the trip?
No, and it does not try. It converts capacities and measured use rates into days, and it reports which reservoir runs out when. Whether an empty reservoir for two days matters, whether wicking can actually keep up with the rate you measured, and whether any of this suits a particular plant are all questions outside arithmetic. A supplier, a local extension service, or someone who has grown the same thing in the same room will be a better source than any calculator.