Project Guides
Long-form guides that explain the measuring, sizing, and buying decisions behind the calculators — written from the same published sources the tools are built on.
The calculators on this site compute; these guides explain. Each one walks through the reasoning behind a common estimating or sizing decision — where the published numbers come from, which conventions are safe to lean on, and where the shortcuts break down — so you understand the answer a calculator gives you, not just receive it.
Every factual claim in a guide traces to the same published manufacturer data and standards the corresponding calculators are verified against, and each guide links the tools that do the arithmetic.
All Guides
Topping Up Attic Insulation: Buy the Shortfall, Not the Target
How to read the insulation already in your attic, pick a target R-value, and turn the shortfall into bags using manufacturer coverage charts.
Updated August 9, 2026
Cord vs. Face Cord: Buying Firewood Without Getting Shorted
What a legal cord of firewood is, why a face cord’s value hinges on piece length, how to measure a delivered stack, and how to compare wood by heat, not volume.
Updated August 9, 2026
Deck Framing Spans 101: How the Load Gets to the Ground
The load path from decking to soil, what the IRC R507 span tables assume, how species and spacing change spans, and where prescriptive deck design ends.
Updated August 9, 2026
How Much Paint Do I Need? A Room-by-Room Walkthrough
How to measure walls, subtract doors and windows, pick a realistic spread rate, and decide on primer and coats — so you buy the right number of gallons.
Updated August 9, 2026
Why Your Boat Won’t Go Faster: A Diagnosis in Three Numbers
Why displacement hulls hit a wall at 1.34·√LWL, what Crouch’s formula says planing speed costs, and how prop slip diagnoses a slow boat.
Updated August 9, 2026
Pool Water Balance Basics: Gallons, ppm, and Four Levers
Why every pool dose starts with your gallons, what ppm really means, which chemistry levers you can raise by the pound, and why lowering pH is different.
Updated August 9, 2026
Why Your Room Sounds Bad: One Room, Two Problems
Room modes and reverberation time in plain terms — why small rooms have lumpy bass, what RT60 targets mean, and where the Schroeder frequency splits the job.
Updated August 9, 2026
Window AC Sizing: The ENERGY STAR Method, Explained
How the ENERGY STAR room-AC table works, what the sun, occupancy, and kitchen adjustments really adjust, and why an oversized unit leaves a room clammy.
Updated August 9, 2026