Builder’s glossary
Every term here appears on one of these calculators — in a field label, a ticket line or a warning. If a word confused you on a tool page, this is where it is explained, and there is a link back to the page that used it.
- Actual size
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What a piece of material really measures, as against what it is called. A "2 × 4" is 1.5 × 3.5 in; a nominal 8 × 8 × 16 in block is 7.625 × 7.625 × 15.625, the missing 3/8 in being the mortar joint. Calculators that count courses must use actual sizes; calculators that count blocks per square foot use nominal, because the nominal size already includes the joint.
- Batter
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The backward lean built into a retaining wall, expressed in degrees. It puts the wall’s weight over its own base rather than out in front of it. A battered wall is shorter at the front face than its height suggests, which is why a batter changes the block count.
- Bevel
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The angle the saw blade is tilted from vertical. Distinct from the miter, which is the angle the workpiece is swung across the table. Crown molding needs both at once, and neither of them is the angle of the corner.
- Board foot
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A volume, not an area: 144 cubic inches of lumber, which is a piece 1 in thick by 12 in wide by 1 ft long. Hardwood is sold by it. Thickness is quoted in quarters of an inch — 4/4 is one inch, 8/4 is two — and it is the rough sawn thickness that is charged for, not the surfaced one.
- Cold joint
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The seam left where fresh concrete is poured against concrete that has already begun to set. It is a plane of weakness, and it is where the crack will go. Avoiding one is the real constraint on mixing a pour from bags rather than ordering a truck.
- Course
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One horizontal row of masonry units with its bed joint. Wall height divided by course height gives the number of courses, and it almost never divides evenly — which is why a wall height is usually chosen to suit the block rather than the other way round.
- Coverage rate
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How much area a unit of material covers: square feet per gallon, per box, per bag. It is published by the manufacturer and it is not derivable — which is why every coverage figure on this site is cited to a data sheet rather than calculated.
- Cubic yard
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27 cubic feet. The unit bulk material is sold in across North America, and the reason so many calculators on this site end in a two-decimal number: nobody sells a partial yard, but knowing you need 1.36 of them tells you whether to order one or two.
- Deduction
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Area taken out for an opening. A standard door is 21 ft² and a standard window 15 ft², figures this site takes from the paint constants and shares with the drywall tools so the two cannot drift. Whether to deduct at all is a trade question: you do not paint a doorway, but plenty of hangers board straight over one and cut it back afterwards.
- Face shell
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The outer wall of a hollow concrete block. ASTM C90 sets a minimum thickness for it, which is what makes the volume of the hollow core calculable — a grouted core is the block’s outside dimensions less two face shells and the webs between them.
- Frost line
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The depth to which ground freezes in a given place. A footing above it will be lifted by frost heave and dropped again every winter until something breaks. The depth that governs is your local code minimum, which is a legal figure rather than a physical one and differs between adjacent jurisdictions — which is why this site asks you for it rather than looking it up.
- Guillotine cut
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A cut that runs the full width or length of the piece being cut, edge to edge. Panel saws can only make guillotine cuts, so a cutting plan for sheet goods has to be composed entirely of them — which rules out layouts that would nest more efficiently and is why optimal panel packing is a hard problem rather than a tidy one.
- Joint compound
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The filler that hides drywall joints and fastener heads, applied over three coats. Sold as conventional (heavy, sands hard) or lightweight (covers the same board at roughly half the weight). Quantity is an estimating convention rather than a physical constant: it moves with finish level, joint count, and how much you scrape back off.
- Kerf
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The width of material a saw blade removes. It sounds negligible and is not: a sheet cut into eight strips loses seven kerfs, and a plan that ignores them produces a last piece that is short by exactly the amount nobody accounted for.
- Lift
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One continuous pour or one continuous fill, placed before the previous material sets. Grouting a block wall is done in lifts for the same reason concrete is: stopping and restarting leaves a joint where there should be none.
- Miter
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The angle the workpiece is swung across the saw table. On a plain 90° corner in flat trim it is 45°. On crown molding it is not — a 38° spring crown meeting a square corner is cut at 31.62° miter and 33.86° bevel, and no part of that is guessable.
- Nominal size
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The name a material is sold under, which is not its measurement. Lumber is nominal before it is dried and surfaced; masonry is nominal including its mortar joint. The difference is not a rounding error and it is not consistent between materials, so it has to be looked up rather than assumed.
- On centre (o.c.)
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Spacing measured from the centre of one member to the centre of the next, rather than the gap between them. Studs at 16 in o.c. have about 14.5 in of clear space. Every fastener schedule and every stud count on this site is quoted o.c., because that is how framing is set out and how codes are written.
- Pitch
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Roof slope, quoted as rise in inches per 12 inches of horizontal run. A 6 in 12 roof rises 6 in for every foot across. Pitch is what makes a roof’s surface area larger than its footprint, and ignoring it is the commonest way to under-order shingles.
- Pot life
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How long a mixed two-part product stays workable. Epoxy grout has one measured in tens of minutes, which is why it is mixed in units rather than by the bucket, and why a kit you opened and did not finish is not a kit you have.
- Purchase count
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The number of whole packages you have to buy, as against the quantity you need. It always rounds up, on every calculator here, without exception — you cannot buy nine tenths of a bag, and rounding the other way is an order that stops work.
- Rise and run
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The vertical and horizontal parts of a slope. A wheelchair ramp at the ADA maximum is 1 of rise to 12 of run; a stair, a roof and a drain all express their slope the same way, in different ratios.
- Settling
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The depth loose material loses after it is spread and rained on. Mulch settles enough to matter, which is why an order carries an allowance on top of the spread volume — a mulch layer that has settled below about two inches has stopped suppressing weeds, which was the point of it.
- Short-load fee
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What a concrete plant charges for sending a truck out with less than its minimum load. It is a fixed sum, so it is decisive on a small pour and irrelevant on a large one — which is why the bags-versus-truck answer flips sharply rather than sliding.
- Spring angle
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The angle at which crown molding sits away from the wall, set by the profile of the moulding itself rather than by the room. 38° and 45° are the two stock crowns. It is the number that turns a corner angle into a miter and a bevel, and it is printed on the moulding’s packaging and nowhere else.
- Square (roofing)
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100 square feet of roof. Shingles are sold in bundles that make up a square, usually three to one, and everything a roofing supplier quotes is per square rather than per bundle or per foot.
- Waste factor
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The percentage added to a quantity for offcuts, breakage and error. It is not one number: tile laid straight wastes less than tile laid diagonally, which wastes less than herringbone. Every waste factor on this site is stored per material and per pattern rather than applied as a blanket ten percent.
- Web
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The internal divider between the hollow cores of a concrete block. Together with the face shells it is what the block’s published minimum dimensions describe, and subtracting both from the outside dimensions is how the volume of grout a core takes is arrived at.
- Yield
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The volume of finished material a package produces, as against what it weighs. An 80 lb bag of concrete mix yields 0.6 cubic feet. Yield is what you count with; weight is what you have to carry, and the two lead to very different conclusions about the same order.
A word about the numbers in here
Where a figure appears above — 27 cubic feet to a yard, 0.6 cubic feet from an 80 lb bag, 21 square feet for a door — it is a value already held in this site's constants file and already used by a calculator. No number was introduced to write this page. The methodology page explains where each class of constant comes from and what happens when one turns out to be wrong.