Shadow Analysis Duration Calculator

Work out shadow analysis duration instantly with clear inputs, formula shown and shareable results.

About Shadow Analysis Duration Calculator

Shadow length is building height divided by the tangent of the sun's altitude. Because the tangent falls steeply at low sun angles, a thirty metre building casts a thirty metre shadow at 45 degrees but a sixty-four metre shadow at 25 degrees, which is why winter overshadowing assessments use the low midwinter sun.

Formula

Shadow length

Length = building height / tan(sun altitude)

Worked example

With the default values below, Shadow Analysis Duration Calculator returns Shadow length of 64.34. Change any input above and every figure here is recalculated in your browser.

Inputs used

Building heightminimum 0.1 m: 30 m
Sun altitudeaccepts 1–89 °: 25 °
Building width facing the sunminimum 0.1 m: 20 m

Results

Shadow length: 64.34 m
Approximate shadow area: 1,286.7 m²
Shadow length to building height ratio: 2.145
Shadow length if the sun were twice as high: 25.17 m

Step by step

1Values used
2Shadow length
3Shadow length= 64.34 m
4Approximate shadow area= 1,286.7 m²
5Shadow length to building height ratio= 2.145
6Shadow length if the sun were twice as high= 25.17 m

Assumptions and limits

The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
Preliminary estimate only. Daylight and overshadowing assessment requires full solar geometry modelling against the applicable guidance.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Preliminary estimate only. Daylight and overshadowing assessment requires full solar geometry modelling against the applicable guidance.

Frequently Asked Questions

How is the Shadow Analysis Duration figure worked out?

Length = building height / tan(sun altitude). Shadow length is building height divided by the tangent of the sun's altitude.

Which date should overshadowing be assessed on?

Usually the winter solstice or the equinox, depending on the local guidance. The winter solstice is the worst case; the equinox is a common compromise for daylight and sunlight assessments.

What values do I need to enter?

This calculator takes 3 inputs: Building height, Sun altitude, Building width facing the sun. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.