Forty gallons of sap. What does tonight actually make?
Your refractometer's sugar reading through the Rule of 86 — the constant is yours to set — then what the run yields, how long your rig boils it, what the fuel costs, and the bottles it fills. Everything stays in your browser.
The sap
The boil
The numbers here are yours to check. This page does arithmetic on what you type — it cannot see your recipe, your equipment or your batch.
For anything you will eat or sell as food, double-check it against your own process and your local rules. This page does maths, not food safety.
Want it to remember?
In MadeKeeper each run is a batch: the fuel logs as a real expense, the bottles land in inventory at their true cost, and the sugarhouse's whole season — sap, boils, bottles, markets — adds up in one honest ledger. See for farmstands & sugarmakers or poke around the live demo. $19/mo for the whole back office, kept for as long as you stay. The shop stays free for cost a piece and one fair — no product cap. The tax packet, Etsy and Square, and more fairs are the $19.
The sums every sugarmaker does on the shed door
Sap in the tank, a February night ahead — every sugarmaker runs the same three sums: what it makes, how long it boils, what it costs. The math below is the same math the calculator runs, constants named and yours to change.
What is the Rule of 86?
The sugarmaker's oldest shortcut: divide 86 by your sap's sugar percentage and you get the gallons of sap that make one gallon of syrup. Two-percent sap — a typical good day — is 43 to 1; sweet three-percent sap is under 29; a thin 1.5% year is 57. The 86 itself is a convention: UVM's Proctor center revised it to 87.1 for modern density targets, which is exactly why the constant is a setting here rather than a number we assert.
How long will tonight's boil take?
The water leaving divided by your rig's evaporation rate — and that rate is a measured, personal number no calculator should invent. A turkey-fryer pan might evaporate a gallon an hour; a good backyard evaporator four to eight; a commercial rig far more. Boil one run with a watch and a dipstick and you own the number forever. Forty gallons of 2% sap has about 39 gallons of water to remove: at four gallons an hour, that is a ten-hour night, which is why sugarmakers nap in chairs.
What does a gallon of my syrup actually cost?
Fuel is the honest place to start, because sap from your own trees arrives free and the boil is where the money burns. Ten hours of propane at $3.50 an hour is $35 against a single gallon of finished syrup — 27 cents a bottle in fuel alone at 8-ounce fills, before jugs, filters, and the evaporator's own cost. This is the number that explains real syrup's price to anyone scandalized by it.
When is it syrup?
When it reaches finished density — and the exact number is your state's law and your hydrometer's job, not this page's. Legal minimums are set in °Brix and enforced at inspection; a syrup finished thin can ferment, finished heavy it crystallizes. Record the density you finish to, test with your own instruments, and treat any calculator that claims to know your state's number with suspicion — including this one, which is why it does not.