How this calculation works
Subtract the boundary inset at both ends of each dimension, then count whole rectangular footprints and the gaps between them. Compare two aligned uniform orientations only. Enter projected plan-view footprints and appropriate gaps; shading/tilt requirements are not inferred.
Whole rectangles along an axis = floor((usable span + gap)/(footprint + gap)), if one footprint fitsA worked example
For a 30 × 20 m site, 2 m insets, 2 × 1 m footprints, 0.2 m within-row gaps and 0.5 m between-row gaps, the entered orientation fits 121 rectangles and the rotated one 126. At entered 550 W each, 126 panels sum to 69.3 kW DC nameplate.
Good to know
Projected rectangular footprints and supplied gaps/insets only. No shadow, tilt, mounting, structural, electrical, fire-access, maintenance or regulatory design. The higher of two uniform orientations is not globally optimal packing. Entered-nameplate kW is not energy generation, an AC rating or a return forecast.
Reference: NIST: exact international-foot and acre factors (opens in a new tab) ↗
Check the land-unit definitions and sources
The standard factors use the international foot and an acre of 43,560 sq ft. Cent means 1/100 acre; gunta means 1/40 acre; the selected Chennai ground means 2,400 sq ft.
The Assam report defines bigha as 14,400 sq ft, katha as 2,880 sq ft and lecha as 144 sq ft. The cited West Bengal court order mentions a 720-sq-ft katha convention. These are explicit presets, not an automatic definition for every record or every place using the same name. Match your record to the stated convention, or use its verified custom factor.
- NIST: exact international-foot and acre factors (opens in a new tab) ↗
- API Setu MDDS: acre/cent and acre/gunta relationships (opens in a new tab) ↗
- Greater Chennai Corporation: one ground is 2,400 sq ft (opens in a new tab) ↗
- Government of Assam AIRBMP framework: section 7.2, page 28 (bigha, katha and lecha) (opens in a new tab) ↗
- Supreme Court order, 7 May 2025: paragraph 2, page 2 (West Bengal katha) (opens in a new tab) ↗
The acre relationships are converted using exact base factors. Rounded or unrelated regional values in a reference table are not substituted for these definitions.
Rectangles need space for the gaps between them
With n footprints along a row there are n−1 internal gaps, not n. Solving n×footprint + (n−1)×gap ≤ usable span gives the count formula used here. One whole footprint must fit before a positive row or column count is returned.
The example site leaves 26 × 16 m after its 2 m boundary insets. With a 2 m along-row footprint, 1 m cross-row footprint and gaps 0.2 m and 0.5 m, the entered orientation has 11 columns and 11 rows. Turning the footprint gives 21 columns and 6 rows, for 126 rectangles.
Those are two uniform aligned layouts only. A mixture of orientations, different corridors or a different site outline could give another result. The higher-count option does not claim to solve global rectangle packing or a solar-site design problem.
Use projected footprints and distinguish power from energy
Enter the actual plan-view footprint and appropriate clear gaps for the model. A panel’s physical length measured along a tilted surface is not automatically its horizontal footprint. This tool does not calculate tilt projection, mounting envelopes, shadows or required row separation.
At an entered 550 W DC nameplate value, 126 rectangles correspond to 69.3 kW DC nameplate. That is a multiplication of supplied rating and count, not kWh generation, an AC output rating, a production forecast or a financial return.
The India land area converter can help understand an area quotation, but area alone does not determine rectangle fit. A long narrow acre and a more compact acre can have different arrangements once footprint dimensions, gaps and insets are considered. The measured shape remains part of the input.
A few questions, answered
Does the tool recommend panel products or a system size?
No. Footprints, ratings and gaps are editable assumptions. No product, electrical or installation recommendation is made.
Is the row gap the same as row pitch?
No. Here the gap is clear distance between adjacent footprint edges. Pitch includes the footprint dimension as well.
What if an inset leaves less space than one footprint?
That orientation returns zero panels and zero occupied array dimensions; a partial panel is not counted.