L-Shape Square Footage Calculator
Enter the two rectangles that make up the room and get square feet, sq m, sq yd, acres, and sq in — plus the checks that catch a double-counted corner.
Last updated:Tip: If you only have the diameter, divide by 2 to get the radius.
L-shape = two rectangles sharing a corner.
Add one row per rectangle and we'll sum them.
How the L-Shape Tab Works
The tab has four number fields and one unit dropdown. It calculates (L1 × W1) + (L2 × W2) and nothing else — no subtraction, no perimeter, no third rectangle. Three details people get wrong are worth reading before you type:
- One dropdown, same unit for all four fields. The selector sits beside the Rect 2 width box, which makes it look like a per-field control. It is not: it sets the unit for Rect 1 as well. To mix feet and inches, use the Irregular tab, which gives each row its own unit.
- Any blank or zero field wipes the result. All four values must be positive; one empty box replaces the total with a dash instead of treating that wing as zero.
- The preview is arithmetic, not your floor plan. The drawing stacks Rect 2 on top of Rect 1, left-aligned, whatever the room looks like. Two rooms with the same two rectangles produce the same drawing and the same area even when one has its notch on the left.
It opens prefilled with 16, 8, 8, 6 in feet — the worked example below — so switching to this tab shows 176.00 immediately.
Worked Example: A 16 × 14 Room With an 8 × 6 Notch
An open-plan kitchen and dining area: the main strip is 16 ft × 8 ft, and the dining wing adds 8 ft × 6 ft at one end. Enclose the whole room and you get a 16 × 14 ft box with a missing corner.
| Route | What you enter (or compute) | Arithmetic | Area |
|---|---|---|---|
| Split across | 16 × 8 and 8 × 6 | 128 + 48 | 176 sq ft |
| Split vertically | 8 × 14 and 8 × 8 | 112 + 64 | 176 sq ft |
| Bounding minus notch | on paper only | 224 − 48 | 176 sq ft |
Three routes, one number. What the widget shows for that total:
| Square feet | Square meters | Square yards | Acres | Square inches |
|---|---|---|---|---|
| 176.00 | 16.35 | 19.56 | 0.004 | 25344 |
The acre line reads "0.004" rather than "0.0040" because the tool trims trailing zeros, and the square-inch line carries no thousands separator. With the default 10% waste factor the same room orders 193.60 sq ft — the waste field applies to the finished total, so add your rectangles first and set the percentage second.
Split Direction Does Not Change the Answer
Any straight cut through the inner corner turns an L into two rectangles, and every legal cut gives the same sum. In the example room, cutting along the 8 ft line gives 128 + 48; cutting perpendicular gives 112 + 64; both are 176. That invariance is a checking tool, not a curiosity: run the split two ways on your sketch and compare. If the totals disagree, one of your four numbers is not what you think it is.
Choose the split whose dividing line you can physically measure — a change of flooring, a wall return, the edge of a beam pocket. Guessing where the corner falls is how a 176 sq ft room becomes a 240 sq ft order.
The Shared Corner Double-Count
The most expensive L-shape error is also the easiest to make. Measure each leg from the outside walls, walking the tape around the room, and you will naturally record the long leg as 16 × 8 = 128 sq ft and the other leg as 8 × 14 = 112 sq ft. Enter both and the tab reports 240 sq ft.
The room is not 240 sq ft. Those two legs overlap in the 8 ft × 8 ft square at the junction — the shared corner — which sits inside both readings. The correct total is 128 + 112 − 64 = 176 sq ft, so the double-count inflates the order by 64 sq ft, about 36%.
The sanity check takes ten seconds and needs no formula: an L-shaped room can never exceed its bounding rectangle. Here that box is 16 × 14 = 224 sq ft, so any total above 224 is wrong before you check a single measurement. Draw the box, mark where each leg stops, and make sure the two rectangles meet at the inner corner rather than crossing it.
Check the Corners Before You Trust Two Rectangles
Rectangle math assumes right angles. Measure the diagonals of the bounding box: for a 16 ft × 14 ft outline the diagonal should be √(16² + 14²) = 21.26 ft. Measure both corners; if the two diagonals differ by more than about half an inch, the room is out of square and the true area is a little under what the rectangles report, because a sheared parallelogram holds less than the rectangle it pretends to be.
For perimeter work — skirting, laminate underlay, a fence run around a tapered lawn — the L-shape outline still obeys P = 2 × (16 + 14) = 60 ft: the stair-step edges add up to exactly the two sides they replace, no matter where the inner corner sits. The tab does not output this; it is a hand calculation, and square feet to linear feet covers the conversion when you start from an area instead.
When Two Rectangles Are Not Enough
- T-shape or cruciform rooms need three pieces: use the Irregular tab and add a row per rectangle.
- An L with a bay window is not two rectangles either — enter the bay as one row of its mid-width, as shown on the irregular page, rather than squaring it off.
- A room with a column, stairwell, or closet cut out of the middle cannot be handled here at all; measure around it and subtract on paper.
- Whole-floor totals belong in the multiple rooms calculator, and materials with offcuts belong in the flooring or tile calculators.
Frequently Asked Questions
How do I calculate the square footage of an L-shaped room?
Cut the L into two rectangles along its inner corner, take length × width for each, and add. The example room is 16 × 8 = 128 sq ft plus 8 × 6 = 48 sq ft = 176 sq ft. Enter the four numbers above and the tab does the arithmetic.
Which split should I use for an L-shaped room?
Either. Across the notch gives 128 + 48, perpendicular to it gives 112 + 64, and both are 176 sq ft — the split never changes the area, only which walls you have to reach. Pick the split whose dividing line you can actually measure, then run the other one as a check.
What if my L-shape total is larger than the room's bounding rectangle?
You have counted the shared corner twice. Entering 16 × 8 (128 sq ft) and 8 × 14 (112 sq ft) reads 240 sq ft, but the 8 × 8 square where the two legs overlap is inside both, and the room cannot beat its 16 × 14 = 224 sq ft box. Subtract the 64 sq ft overlap: 240 − 64 = 176 sq ft.
Can I enter one rectangle in feet and the other in inches?
No. The L-shape tab has a single unit dropdown — it sits beside the Rect 2 width box, but it sets the same unit for all four fields. Convert by hand, or use the Irregular tab, which has a unit selector on every row.
Can the L-shape calculator subtract the missing corner?
No. It only computes (L1 × W1) + (L2 × W2) and ignores negative entries. Use subtraction as a paper cross-check: 16 × 14 = 224 sq ft, minus an 8 × 6 = 48 sq ft notch, equals 176 sq ft — the number the tool should be showing you.
What happens if I leave one of the four fields blank?
The result clears to a dash. All four fields must be positive numbers, so one empty box cancels the whole calculation. That is deliberate and it differs from the Irregular tab, where a half-filled row is skipped silently while the remaining rows still total.
Does the L-shape tab give me the perimeter?
No — area only. For a rectilinear L the perimeter is still 2 × (16 + 14) = 60 ft, because the stepped edges make up exactly the two sides they replace. Measure the legs directly for skirting or trim, and see square feet to linear feet when you are working from an area.
Sources and How to Check This Page
- Every unit conversion shown here comes from NIST Special Publication 811, Appendix B.9.1: 1 ft = 0.3048 m exactly, so 1 sq ft = 0.09290304 m²; 1 sq yd = 9 sq ft and 1 acre = 43,560 sq ft are exact by definition. 176 × 0.09290304 = 16.35 m² and 176 ÷ 9 = 19.56 sq yd.
- The foot those factors rest on is defined in 85 FR 62698, which fixes the international foot at 0.3048 m and deprecates the US survey foot as of December 31, 2022.
- The double-count and the perimeter rule are pure geometry and you can check them on graph paper: 128 + 112 − 64 = 176, and the 16 × 14 outline walks 16 + 8 + 8 + 6 + 8 + 14 = 60 ft. The diagonal is Pythagoras: √(16² + 14²) = √452 = 21.26 ft.
- The widget statements — one unit dropdown applied to all four fields, the 16/8/8/6 prefill, the all-or-nothing validation that clears the result when any field is blank, waste applied to the summed area, and the left-aligned stacked preview — were read out of
templates/partials/calculator-core.html,js/calc-ui.js, andjs/calc-canvas.jsrather than inferred from the screen. - What this page does not claim: no perimeter output, no subtraction of openings, no reverse solve for a missing side, and no material-specific waste percentages — those come from your installer or supplier, not from a standard.