Why the two depths differ
Ice floats, and it floats because a given weight of water takes up more room frozen than liquid. Put a figure on it with the two densities in the form: at 62.4 lb per cubic foot for water and 57.2 for ice, a cubic foot of water becomes 62.4 / 57.2 = 1.091 cubic feet of ice. So 1.25 in of finished ice comes from 1.146 in of water, and over a 16,327 sq ft sheet that is 1,559 cubic feet, or 11,662 gallons, before anything is lost to the drain.
Add the six per cent that runs off the edges and evaporates and the meter sees 12,407 gallons for that build. Thirty-gallon errors do not matter. The eight per cent does, because it runs through every one of the forty-odd floods.
Where the corners go
A 200 by 85 rectangle is 17,000 square feet. Round the four corners at a 28 ft radius and each corner loses the difference between a quarter of a square and a quarter of a circle, which comes to 673 square feet across all four — four per cent of the sheet, and four per cent of every flood you ever lay on it. Measure the radius off the dasher line rather than guessing it; rinks built to different eras of the same rule book have visibly different corners.
Build floods are not resurfacer floods
The 300 gallon default here is a hose flood, the kind used to build a sheet from bare floor, and it puts down about three hundredths of an inch at a time. A resurfacer laying 130 gallons on a finished sheet puts down less than half that. Both are in the same arithmetic; only the tank size changes.
What this cannot know
It cannot tell you what thickness to build to. That comes from whoever governs play on your sheet, or from your own house standard, and the field is there for you to type it into. It cannot tell you whether the floor under the ice is flat, and an uneven floor means the average thickness this page works out is spread unevenly over the sheet — that is a survey question, not an arithmetic one. And it has no view on how fast you can lay the floods, which is a plant question.
Questions people ask
Why does 1.25 in of ice not take 1.25 in of water?
Because water expands as it freezes. The mass is the same but the volume grows by roughly eight per cent, so a shallower layer of water becomes a deeper layer of ice. The two densities you enter set the ratio; at 62.4 and 57.2 lb per cubic foot it works out at 1.091 to 1.
Should I use a hose or the resurfacer to build?
That is your call and depends on the machine, the sheet and how many people you have. The calculator does not care which — it asks how many gallons go down in one flood, and you can put a hose flood or a machine flood in that field.
What thickness should I build to?
This page has no figure for that and will not offer one. It comes from the body that governs play on your sheet, from your engineer, or from your own operating standard. Type yours into the target field.
Why is my meter reading higher than the answer?
Losses. Water at the edges runs to the drain, a warm sheet evaporates, snow on the ice soaks some of it up, and hoses drip. Track the meter against the depth gauge over a week of building and replace the default loss share with what you actually measure.
Does the corner radius really matter?
Four per cent of a sheet is four per cent of every flood for the life of the ice. On a 200 by 85 with 28 ft corners that is 673 square feet of ice you would otherwise be paying to freeze.