Terms of use

Who you are dealing with

This site is operated by Eioto Studio, contactable at tsuyoshi.gt@gmail.com. These terms apply to every page on doorslesson.com.

The calculators are estimates, and here is exactly why

Every figure this site produces is an estimate for planning and budgeting. It is not a specification, not a structural design, and not a quantity take-off you should hand to a supplier without checking. We are specific about this because the reasons are specific:

• Yields vary by product. We name the coverage or yield figure each calculator uses and where it comes from, but an 80 lb bag of one manufacturer's mix does not yield the same volume as another's, and a mulch supplier's cubic yard is not always a full cubic yard. Read the bag or the delivery ticket.
• Sites are not rectangles. A slab is thicker where the subgrade dips. A wall has openings. A lawn has a curve you measured as a straight line. Real quantities run above the geometric ideal, which is why waste allowances exist and why they are a field you can change.
• Compaction, shrinkage and moisture move the answer. Gravel settles, soil shrinks, mortar joints absorb, timber moves. A calculator cannot see your material's condition.
• Nothing here is engineered. If a quantity depends on load, span, drainage, frost depth, or fire and structural code, it needs a licensed engineer or your local building department, not a web page. That includes slab thickness, reinforcement, footing sizes and retaining walls.

Treat a result as a starting point to sanity-check against a supplier's own figure and your own measurements. Measure twice on site before ordering anything that cannot be returned.

No warranty

We work hard on the arithmetic — each formula is checked against a published source, and the source is named on the page — but the site is provided "as is", without warranty of any kind, express or implied, including fitness for a particular purpose. We do not warrant that a calculator is free of error, that a cited yield figure still matches a manufacturer's current product, or that the site is available without interruption.

Limitation of liability

To the fullest extent permitted by law, Eioto Studio is not liable for any loss arising from your use of this site. That expressly includes material ordered in the wrong quantity, delivery and restocking charges, wasted labour, delay, remedial work, and any consequential or indirect loss. You are responsible for the decision to buy and the decision to build.

Nothing in these terms limits liability that cannot lawfully be limited — including liability for death or personal injury caused by negligence, or for fraud. If you are a consumer, your statutory rights are unaffected.

Tell us if a number looks wrong

This is the one request we make of you. If a result does not match what you measured on the job, email tsuyoshi.gt@gmail.com with the inputs you used and what you actually needed. Corrections take priority over new pages, and a report from someone who has done the work is the most valuable thing we receive.

Using the content

The text, formulas as expressed here, layout and code are © Eioto Studio. You are welcome to:

• use the calculators for your own projects, commercial ones included;
• quote a figure or a paragraph with a link back to the page it came from.

You may not republish pages wholesale, scrape the site to generate a competing calculator set, or present our content as your own. Underlying engineering facts and public yield figures belong to nobody; our explanations of them are ours.

Advertising

Pages carry advertising served by Google AdSense, which is what pays for the site. We do not choose the individual ads and an ad is not an endorsement of the advertiser, their product, or their price. If a calculator ever recommends a specific product, it is because it is the right product, and we will say so plainly. See the privacy policy for the cookies advertising involves and how to opt out of personalisation.

Links out

We link to manufacturers, standards bodies and building departments as sources. We do not control those sites and are not responsible for their content or their accuracy.

Changes and governing law

We may update these terms; the revision date below changes when we do, and continuing to use the site means accepting the current version. These terms are governed by the laws of Japan, where the operator is based, without affecting any mandatory consumer protection of your country of residence. The current version is dated 2026-07-30.