Guides.

The reasoning behind the numbers on the tags — written from building the calculators, and checkable against the label on your own can.

A calculator gives you a quantity. It cannot tell you whether you measured the right surface, whether the coverage rate on your product matches the default it assumed, or whether the number it produced is a shopping list or a structural plan. These guides cover that part — the decisions around the arithmetic, where the real money is won and lost.

01
How much paint do you actually need

Why 350 square feet per gallon is only a starting point.
8 min read
02
How to measure a room properly

The step before every calculator, and the one that costs the most when it goes wrong.
8 min read
03
Why you buy 10% more flooring than your room

Waste allowance is material the installation really uses. What sets the number.
7 min read
04
Sizing an air conditioner: what BTU actually means

Bigger is worse. Why oversizing an air conditioner makes a room clammy instead of cool.
7 min read
05
Mulch and gravel: yards, bags and tons

Cubic yards, 2-cubic-foot bags and tons: three units for the same pile, and how to move between them.
7 min read
06
Deck and fence material lists, from first principles

How the counts are derived, and the questions a material list deliberately leaves to your building department.
8 min read
07
How to read a coverage label

The number on the can is a laboratory result. How to translate it into your room.
6 min read
08
Wire size, breakers and voltage drop

Two questions decide a wire size, and only one of them is on the table.
11 min read
09
Does my panel have room for it

Full of breakers and short of amps are different problems with different fixes.
10 min read

Straight to a tool

If you already know what you are estimating, all 18 calculators are on the board: