How does the bathroom floor slope calculator work?

It takes the run from the farthest point of the floor to the drain and a slope ratio written as 1:D, then computes the fall by dividing the run by that denominator. A 1:80 slope over a 1,500 mm run gives about 19 mm of fall. It also shows the slope as a percentage, the fall per metre, and the screed depth rising from the drain to the high point.

What floor slope should a bathroom have in India?

Most bathroom floors work well at a fall between 1:100 and 1:80, which is roughly 10 to 12.5 mm of drop per metre toward the drain. Tight shower or wet zones can go steeper, up to about 1:50. Anything flatter than 1:100 tends to pond water and stay wet, so it is usually avoided on wet floors.

How accurate is this calculator and what should I verify?

Treat the numbers as indicative for planning, not a construction drawing. Measure the straight diagonal line from the farthest corner to the drain, since that is the longest fall path. Actual screed build-up depends on your slab level, tile thickness and drain position. Confirm the final slope, screed depth and continuous waterproofing with your site engineer or mason before casting.

Floor Slope Calculator

Bathroom Floor Slope Calculator

Enter the run from the farthest point to your drain and a slope ratio. Get the floor fall in mm, the screed depth at the high point vs the drain, the slope %, and a drains-properly verdict. Indicative India 2026 — confirm with your site engineer.

Your floor & fall

Distance to drain (mm)

Slope ratio (1:D)

12.5 mm fall per metre. The usual whole-bathroom slope in India.

Min. screed at drain (mm)

Large floor — split into two slope planes

Diagonal tip: the farthest point is usually the diagonal corner, so measure the straight line from that corner to the drain — not along the wall. Splitting a big floor into two planes keeps the screed from building up too thick at the high point.

Fall = run ÷ ratio. Screed sits thinnest at the drain and thickest at the high point. Keep waterproofing continuous over the whole fall and lap it up the walls. Indicative — confirm slope and screed with your site engineer.

Total floor fall to the drain

0 mm

a 1:80 slope (0 %) over a 1,500 mm fall path

Drains reliably. This meets the usual 1:100-or-steeper wet-area minimum.

Screed at high point

44 mm

thickest build-up

Screed at drain

25 mm

thinnest point

Slope grade

1.25 %

12.5 mm per metre

Fall path

1,500 mm

4.9 ft run

Floor fall (mm) over your 1,500 mm fall path at each standard ratio — your choice highlighted; red is too flat. Indicative — confirm with your engineer.

Get the fall & screed right

Check your slope, screed build-up and waterproofing with DesignAI.

Go deeper

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Estimates are indicative. Actual fall and screed depth depend on your drain position, floor thickness allowance and finish. A 1:100-to-1:80 fall suits most bathroom floors; shower and wet zones can go steeper to 1:50. Always confirm the slope, screed build-up and continuous waterproofing with your site engineer or mason before casting.

Frequently asked questions

How does the bathroom floor slope calculator work?: It takes the run from the farthest point of the floor to the drain and a slope ratio written as 1:D, then computes the fall by dividing the run by that denominator. A 1:80 slope over a 1,500 mm run gives about 19 mm of fall. It also shows the slope as a percentage, the fall per metre, and the screed depth rising from the drain to the high point.
What floor slope should a bathroom have in India?: Most bathroom floors work well at a fall between 1:100 and 1:80, which is roughly 10 to 12.5 mm of drop per metre toward the drain. Tight shower or wet zones can go steeper, up to about 1:50. Anything flatter than 1:100 tends to pond water and stay wet, so it is usually avoided on wet floors.
How accurate is this calculator and what should I verify?: Treat the numbers as indicative for planning, not a construction drawing. Measure the straight diagonal line from the farthest corner to the drain, since that is the longest fall path. Actual screed build-up depends on your slab level, tile thickness and drain position. Confirm the final slope, screed depth and continuous waterproofing with your site engineer or mason before casting.

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