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Squareness Checker (3-4-5 Rule)

Check whether a corner is square using the 3-4-5 rule: compare the measured diagonal to the expected one and read the corner angle.

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Beam Load CalculatorEstimate the maximum moment, deflection, bending stress and demand/capacity ratio of a beam for seven load cases — a preliminary check, not a design.Board Foot CalculatorWork out board feet from thickness, width and length, with quarter notation, metric entry, 30 wood species, moisture content and price.Bolt Torque CalculatorGet the tightening torque of a metric or UNC bolt from its grade, tensile stress area, target preload and lubrication, in N·m and lb·ft side by side.Carpet CalculatorEstimate carpet, padding and installation cost for rectangular, L-shaped or multi-room floors. Measure in feet+inches, inches, yards, metres or centimetres, read the area in ft², yd² and m² at once, price per sq ft or per m², and pick a 12/15 ft US roll or a 4/5 m European one.Lumber Calculator (nominal vs actual size)See why a 2×4 is really 1½ × 3½ inches, then size boards for a deck, a fence, shelving or wall framing with waste and pricing.Miter Angle CalculatorFind the miter (and bevel for crown molding) saw angles for any corner, from the corner angle and spring angle.Pipe Flow Calculator (Hazen-Williams & Darcy-Weisbach)Solve for flow rate, velocity or pressure drop in a full pipe, in imperial or metric units, by Hazen-Williams, by Darcy-Weisbach with an iterated Colebrook-White friction factor, or by both side by side. Reports the Reynolds number and the flow regime — and refuses to print a Hazen-Williams number outside its validity range (water near 15 °C, turbulent flow), which is where most pipe calculators quietly mislead.Rebar CalculatorCount the bars each way in a slab from its size, spacing and cover, then get the laps, the stock bars to buy and the total steel weight.

Open Squareness Checker (3-4-5 Rule) and you get an answer straight away, with no account to create. You will find it under Building & renovation, with Beam Load Calculator and Board Foot Calculator for the neighbouring cases.

How to use it

  1. Open the tool — no signup or install needed.
  2. Enter your input or adjust the available options.
  3. Get your result instantly, then copy or download it.

Frequently asked questions

What does Squareness Checker (3-4-5 Rule) do?

Check whether a corner is square using the 3-4-5 rule: compare the measured diagonal to the expected one and read the corner angle.

When would I actually use this?

Buying the right amount at the merchant: how many tiles, how much paint, how many bags of concrete, and what it all comes to.

What is the most common mistake?

Ordering the exact calculated quantity. Every material loses some of itself between the pallet and the finished job — offcuts, breakage, a bag that sets, a coat that soaks in further than the datasheet says — so add the allowance yours asks for, and order it in one delivery: a second batch rarely matches the first.

How is Squareness Checker (3-4-5 Rule) different from Beam Load Calculator?

They sit next to each other but answer different questions: Beam Load Calculator is the one to open when you need it to estimate the maximum moment, deflection, bending stress and demand/capacity ratio of a beam for seven load cases — a preliminary check, not a design. Pick whichever matches what you're starting from — both are free.

Is there a tool for the next step?

Board Foot Calculator is the closest one after this: Work out board feet from thickness, width and length, with quarter notation, metric entry, 30 wood species, moisture content and price.

What else is worth having open alongside it?

Bolt Torque Calculator and Carpet Calculator — they come up in the same task often enough to be worth a second tab.

Where do the figures come from?

The geometry is exact for the dimensions you enter. Coverage rates come from manufacturer datasheets and vary with the surface, the number of coats and how absorbent the substrate is.

Further reading

All guides →
GuideEstimating a Beam's Safe Load: Span, Deflection and the Load CaseA calculator gives you an order of magnitude, and anything holding up a floor, a roof or people needs an engineer and a code check. Between those two facts there is a great deal worth knowing: which power of the span the deflection really follows, which loading case the tool assumes, and what L/360 is in fractions of an inch on a span you can measure.How-toHow to Calculate a Staircase: Risers, Treads and the Rule That Ties Them TogetherA 110 in rise divided by a 7 in target gives 15.7 risers. You round to 16 and divide again, landing on 6 7/8 in. Here is the whole method, and why the building codes do not agree with each other.GuideWhat a Steel Plate, Bar or Tube Weighs — And What the Number Is ForSection area times length times density, for nine profiles and fourteen metals. What the calculator returns, why one figure covers every carbon-steel grade, and the two places its geometry is not the merchant's geometry.ExplainerTightening a Bolt to the Right Torque: Why the Number on the Wrench Is a GuessTorque does not hold a joint together — preload does, and torque is a poor proxy for it. Here is where 90 % of your effort goes, what the K-factor really is, and why the same 37.84 N·m gives anything from 12.61 kN to 37.84 kN of clamping force.GuideHow Much Lumber a Project Needs — And Why a 2×4 Isn't OneCount pieces first, then linear feet, then board feet. A 2×4 measures 1½ × 3½ inches but is billed on the full 2 × 4 — 34 % of what you pay for is sawdust. Worked from the calculator's real output, with the waste rule it actually applies.GuideMaterials for a Retaining Wall — And the Thing That Actually Makes Them Fall OverBlocks, base gravel, drainage stone, geogrid and pipe, counted from the calculator's own output. Then the number nobody puts in a materials list: a saturated backfill pushes about 2.2 times as hard as a drained one.