Pipe gradient and invert level calculator
Convert pipe gradients between 1 in X, %, degrees and fall per metre, work out the fall over a length, and list invert levels, depth to invert and cover along a drainage run.
Free, no sign-in. Nothing you type is stored or sent anywhere — it's all worked out in your browser.
Invert levels along the run
How this works
Gradient is fall ÷ length. 1 in X = 1/X; % = fall per metre × 100; degrees = arctan(fall per metre).
Fall over a length = length × gradient.
Invert at a chainage = start invert − gradient × (chainage − start chainage). Depth to invert = ground − invert. Cover to crown = ground − invert − pipe outside diameter.
FAQs
How do I convert 1 in 80 to a percentage?
Divide 100 by 80: 1 in 80 is 1.25%, or 12.5 mm fall per metre.
How do I work out the fall over a pipe run?
Multiply the length by the gradient as a decimal. For example, 45 m at 1 in 100 falls 0.45 m.
What's the difference between depth to invert and cover?
Depth to invert is ground level minus the invert level. Cover to crown also takes away the pipe's outside diameter, so it's the depth of soil above the pipe.
Which way does the run fall?
This tool assumes the pipe falls as chainage increases — the usual direction for gravity drainage.
Civvio works this out automatically from your contract and site records.
Upload the contract and keep your diary, and Civvio flags the dates, notices and money at risk on every job — for you to review before anything is sent.
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