Most of a building is decided before there is a model.
Those decisions get made on a sketch, on a call from the field, on a number somebody needs before lunch. This is where a practising architect in New York builds tools for that part of the work. The calculators are live and free. The massing tool is not deployed.
Start with the calculators
Twenty-five of them right now, under the name DATUM. Concrete, rebar, stairs, framing, insulation, roofing, tile, drywall, paint, excavation, retaining walls, and the rest of the arithmetic that stands between a sketch and an order.
Free, no account, no email. They open in a browser, including the one in your pocket, and nothing you type into a calculator leaves it.
The stage before the model
Design software describes a building well once you have committed to one. Free calculator pages return a number in two seconds and tell you nothing about where it came from. Between the two sits the hour in which the building is actually decided: the massing that has to be shown tomorrow, the quantity somebody needs before lunch, the stair that has to work before the plan can be drawn.
Those questions get answered on the back of a drawing set, or they get guessed at. Both tools on this domain are attempts at the same thing. An answer you can check, at the stage where the answer still changes the building.
Four rules, applied to all of them
Every constant names its source. Bag yields cite the manufacturer's technical data sheet. Code limits cite the section number. Conversions use exact legal definitions instead of the rounded factors that get copied from one calculator to the next: one square foot is 0.09290304 m², one pyeong is 400/121 m². A number you cannot trace is a number you are taking on faith.
Imperial output is written the way it goes on a drawing. 13'-9-1/4", with the rounding residual shown, not 13.7708333 ft. A result you have to convert by hand before you can use it is a result you will eventually get wrong.
Right arithmetic is not the same as a right answer. Where the sum is correct and the outcome still fails, the page says so next to the number instead of leaving you to find out on site.
Nothing you type is transmitted. Every calculator runs as JavaScript on the page in front of you. No account, no form, no database, no logging. Closing the tab is the whole delete function.
Every calculator, and what it is for
Drawing and measurement
- Architectural Scale Converter — scaled drawing to real dimension at any imperial, engineering or metric scale, answered in feet and inches to the sixteenth with the rounding residual left visible.
- Area Unit Converter — square metres, square feet, acres, hectares, pyeong and tsubo, converted through the legal definitions rather than the rounded factors.
- Slope and Grade Calculator — percent, ratio, degrees and the fall over a given run. The four ways a drawing states a slope, reconciled.
Structure and layout
- Stair Rise and Run Calculator — risers, treads, total run and stringer length from a total rise, checked separately against IBC 1011.5 and IRC R311.7.
- Roof Pitch Converter — rise-per-12, degrees, percent and rafter multiplier, plus rafter length for a given run.
- Wall Framing Calculator — studs, plates and framing factor, with 16 and 24 inch on-centre set side by side so the trade-off is visible before anything is framed.
- Assembly R-Value Calculator — what a wall delivers once the studs bridge the insulation. Parallel path method, nominal against effective.
Materials and quantities
- Concrete Volume Calculator — slabs, footings and columns in cubic yards and cubic metres, with a waste factor and bag counts taken from published yields.
- Rebar Calculator — bar count and weight for a slab, including the lap splices most calculators leave out, checked against the ACI 318 maximum spacing.
- Tile and Flooring Calculator — tiles, boxes and attic stock, with a waste allowance sized to the lay pattern rather than a flat ten percent.
- Board Feet Calculator — board feet, linear feet and cost, showing the nominal size you are billed for beside the actual size you build with.
- Drywall Calculator — sheets, screws, tape and compound, and what each board length costs you in joints.
- Paint Coverage Calculator — wall area minus the openings, times the coats, rounded up to whole cans, with what is left for touch-ups.
- Roofing Calculator — squares and bundles from a footprint, including the pitch multiplier that makes a roof larger than the house beneath it.
- Concrete Block (CMU) Calculator — blocks, courses, mortar and grout, with the blocks-per-square-foot arithmetic shown rather than assumed.
Site and groundwork
- Excavation Calculator — bank, loose and compacted volumes, so the haul count and the backfill shortfall are both known before the machine arrives.
- Gravel and Aggregate Calculator — volume and tonnage for a driveway or base course, with a compaction allowance and the density figure stated openly.
- Retaining Wall Calculator — blocks, buried base course and drainage stone, and the height at which this stops being a calculator problem.
- Fence Post Concrete Calculator — concrete per hole and bags in total, with embedment checked against the one-third rule and a frost depth warning.
- Mulch and Topsoil Calculator — cubic yards and bags for a bed, at the depth that does the job instead of the depth that looks right.
- Deck Board Calculator — boards, joists and fasteners, with the installation gap that changes depending on whether the lumber arrives wet or already dried.
Where the constants come from
Claiming that everything is sourced is easy, so here is the ledger.
- Stair geometry. IBC 1011.5 and IRC R311.7, cited by section and checked separately, because the two do not set the same limits and a stair can satisfy one while failing the other.
- Rebar spacing. The ACI 318 maximum, applied as a check against the layout you asked for rather than offered as a suggestion.
- Framed wall performance. The parallel path method with a framing factor, which is why the figure it returns is lower than the one printed on the insulation.
- Post embedment. The one-third rule, plus a frost depth warning, because a depth that holds in one climate heaves in another.
- Bag yields. The manufacturer's technical data sheet, by number, not an average of what other calculators assume.
- Unit conversion. Exact legal definitions. One square foot is 0.09290304 m². One pyeong is 400/121 m². Both are exact, and both are usually rounded away.
- Aggregate tonnage. A stated density, shown as the assumption it is rather than folded silently into the result, since that assumption is what decides whether the delivery arrives short.
- Roof area. The pitch multiplier from the geometry, which is why the roof is always larger than the footprint under it.
Codes get amended and manufacturers change their products. A calculator quietly running on a superseded edition is worse than no calculator at all, so the constants get re-checked against their sources instead of being set once and forgotten. Naming the source on the page does the other half of that job: when your jurisdiction amends something, you can see exactly which line to stop trusting.
When the arithmetic is right and the answer is still wrong
This is the part the genre leaves out, and it is most of the reason these exist.
A stair can be perfect on paper and fail inspection. Divide a total rise into a riser count that produces a legal riser and you can still end up with a tread that is short, a headroom that is gone, or a dimension that clears one code and not the other. The number was never the hard part.
The hole will not fill itself. Soil comes out of the ground larger than the space it occupied and goes back smaller once compacted. Order backfill by the size of the excavation and you are short. Haul by the same figure and you pay for trips you did not need. Bank, loose and compacted are three different numbers for the same dirt.
Gravel ordered by volume arrives short. It is sold by weight. Weight follows a density that varies with the material, the gradation and how wet it was when it was loaded. A tonnage calculated from an unstated density is a guess wearing a decimal point.
Walls fail from water, not from a miscount. A retaining wall with the right block count and no drainage stone behind it is a wall on a schedule. Height is the other one: past a certain point the job needs an engineer and a permit rather than a calculator, and the page says where that line falls.
Lumber is billed on the nominal size and built with the actual one. A 2x10 is 1.5 by 9.25 inches in the wall and a 2x10 on the invoice. Board feet follow the nominal figure, framing follows the real one, and both belong on screen at once.
A wall does not deliver the number printed on the insulation. Studs bridge the cavity and conduct around it, so the assembly performs below its nominal rating, and the gap grows wider the better the insulation gets. Specifying to the nominal figure is how a wall misses an energy target on paper that it was never going to hit in the field.
FORMGIVING is the other half, and it is not deployed
The tool the domain is named for does the same job one stage earlier. Draw a site boundary on satellite imagery, choose one of six massing types — podium, vertical, cascading, helix, courtyard, signature — set a floor count up to forty, and the volume stands up in three dimensions on the real map, against the real neighbours, at the real orientation.
The site figures come off the polygon you drew rather than off an assumption: area measured geodesically on the ellipsoid, the longest edge, the bearing that edge sits at, and the gross floor area and FAR your floor count implies. React and MapLibre on the front, FastAPI and Shapely on the back.
It runs on my machine and nowhere else. Not deployed, not in beta, not open for signups. It needs a live backend, so it cannot be posted as static files, and development is paused while the calculators get the attention. There is no list to join and no address to leave, because a waitlist for software with no server behind it is an email list with better manners. If it becomes usable it will appear here, and until then this paragraph is the whole announcement.
Conceptual massing in any case. Not intended for construction, regulatory or legal use.
Who makes this
A practising architect in New York. One person, not a team, not a company, not an agency.
Every tool here started as a question I could not get a trustworthy answer to during real work. That is the whole editorial policy, and it decides what gets built, what gets re-checked, and what gets refused.
You will find no user count on this page, no logo wall, no testimonial from someone who does not exist. That is deliberate. The verifiable thing about a calculator is not how many people have used it. It is whether the constant it used is the one printed in the code book. Every constant here names its source, so you can check the thing itself instead of the popularity of the thing.
What this is not
These are design aids. Not compliance certification, not professional advice, and not a substitute for the person who signs and seals the drawings.
Codes are adopted and amended state by state and town by town. Before you rely on anything here, confirm the edition in force and any local amendment with the authority having jurisdiction. Manufacturer figures move with the product, so check the bag, the box or the data sheet you have in your hand rather than the one that was current when a page was written. Anything that carries real consequence goes to the licensed professional responsible for the work.
The calculators keep what you type inside your browser. What the rest of this domain does with a visit is set out on the privacy page.