Keep two calculations separate: how much sign area is allowed and how much area the proposed design uses. Correct frontage arithmetic can still produce a failed layout if the sign was measured under the wrong definition or existing signs already use part of the allowance.
Read the rule into a worksheet
Record sign category, district, wall or tenant frontage, units, cap, and treatment of existing signs. Confirm whether the allowance belongs to a tenant, building face, or property. Do not borrow another tenant’s frontage or another elevation’s unused allowance without a provision that permits it.
| Formula form | Calculation | Question to resolve |
|---|---|---|
| Linear frontage | Width × allowance per linear foot | Which frontage qualifies? |
| Wall percentage | Eligible wall area × decimal percentage | Which boundaries and exclusions apply? |
| Fixed limit | Stated square-foot allowance | Per sign, face, tenant, or aggregate? |
| Formula with maximum | Smaller of formula result and cap | Is there also a per-sign cap? |
These are reading aids, not a ranking of what municipalities use. Apply the actual formula for the project. Carry alternatives, minimums, or bonuses into the calculation with their conditions rather than treating every number as another allowance to add.
Worked example: frontage with a cap
All dimensions, ratios, and limits in these examples are fictional.Assume a tenant has 48 feet of qualifying frontage, a rate of 1.25 square feet per linear foot, and an aggregate wall-sign cap of 55 square feet.
Frontage calculation: 48 ft × 1.25 sq ft/ft = 60 sq ft. Apply the cap: the smaller of 60 and 55 is 55 sq ft. If an existing sign uses 12 sq ft of that same allowance and remains, the available balance is 55 − 12 = 43 sq ft.
A proposed 10-by-4-foot cabinet uses 40 sq ft under a fictional full-cabinet definition, leaving 3 sq ft. That addresses area only. Quantity, placement, projection, illumination, and individual sign limits need their own checks.
Worked example: a wall percentage
Imagine a different fictional rule that counts a 40-foot-wide by 16-foot-high wall, excludes 80 sq ft of openings, and allows 10% of the remaining area. Eligible wall area is (40 × 16) − 80 = 560 sq ft; 560 × 0.10 =56 sq ft of sign allowance. Exclude openings only because this example expressly says to. A different definition produces a different denominator.
Do not multiply by 10 when the instruction is 10%. Convert it to 0.10. A frontage ratio in square feet per linear foot is not a dimensionless percentage. Keep units visible so someone else can check the calculation.
Two real formulas
San Luis Obispo, California uses the wall-percentage kind. Its section 15.40.470(A)(2) allows wall signs of “a maximum of one hundred square feet or fifteen percent of the building face where the sign is attached, whichever is less,” and computes the building face as frontage times average height. Our wall-sign formula entry works it on two storefronts. For how a real code measures the sign itself, see the Austin case file and one wall sign under three measuring rules, where the same face comes out at 16 or 24 square feet depending on the code. (Read September 28, 2026.)
Measure the proposed copy using the actual definition
For individual letters and logos, ask which enclosing shapes the code requires and whether separate elements can be measured separately. In a fictional layout, two 4-by-2-foot copy groups separated by a 2-foot gap total 16 sq ft as separate rectangles. One rectangle around the complete 10-by-2-foot layout measures 20 sq ft. Neither method is automatically the correct legal method.
Show enclosing lines on the elevation. Identify any cabinet, contrasting background, logo, raceway, or decorative border whose treatment needs confirmation. Measure the final artwork, not only the text height stated on a quote. A 30-inch-high element is 2.5 feet high when calculating square feet.
Submit a calculation someone else can reproduce
- Dimension the qualifying frontage or wall and label exclusions.
- Show the formula, units, intermediate result, caps, and final allowance.
- List retained, removed, and proposed signs sharing that allowance.
- Outline each measured sign area and state the definition used.
- Resolve tenant allocation and multiple-elevation questions before fabrication.
This worksheet teaches geometry using invented conditions; it does not supply a local allowance. Obtain project inputs from the current ordinance and approved site documents. For glass-mounted graphics, use the window-area worksheet, where eligible glass and per-opening treatment need separate confirmation.