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Grade / Slope

What it's for

Turns a rise and a run into a slope, written every way a drawing or an inspector might ask for it: percent, ratio, degrees and inches per foot. It checks the slope against two IRC lines, the maximum for a ramp and the minimum for grade falling away from a foundation, and draws the profile. A PURPOSE row picks the line that fits the job. There is nothing to buy, so there is no material list.

Step by step

The example is the screen as it opens: 6" of rise in 10' 0" of run, PURPOSE Both.

Grade / Slope at its defaults: RISE 6", RUN 10' 0", PURPOSE Both (Ramp and Drainage beside it), RAMP SERVES Egress door (or Other ramp), SURFACE Soil (or Paved). The answer bar reads 5.0%, a green Within 8.3% (1:12) max for the ramp at the egress door (IRC 2021 R311.8.1), and Ratio 1:20 · 2.9° · 0.60 in/ft. RESULTS repeats the ratio and Rise 6" · Run 10' 0" with two green checks, Within 8.3% (1:12) max for the ramp at the egress door (IRC 2021 R311.8.1) and At least 5.0% grade away from the foundation (IRC 2021 R401.3), then the BASIS & WHAT WAS ASSUMED row and the link Check before you cut · Measure twice. 1 2 3 4 5 6
Steps 1 to 5 are the inputs. Everything else on the screen is the answer.
  1. Enter RISE: the difference in height between the two ends, measured plumb. Take it off a level line, a laser or a transit, not by eye along the ground.
  2. Enter RUN: the level distance between the same two points. Measure it horizontally, not along the slope.
  3. Set PURPOSE: Ramp, Drainage or Both. Ramp keeps only the ramp line. Drainage keeps only the foundation line. Both, the default, shows the two of them, and one of them is red whenever the slope is outside 5.0–8.3%.
  4. For a ramp, set RAMP SERVES. Egress door, the default, is the ramp at the door the code requires you to have: it may slope at most 1:12 (8.3%). Other ramp is any other ramp — a garage, a shed, a second door — and may slope up to 1:8 (12.5%). Both limits are IRC 2021 R311.8.1.
  5. For drainage, set SURFACE. Soil, the default, must fall 6" in the first 10' (5%). Paved is a patio, walk or drive within 10' of the foundation, which IRC 2021 R401.3 lets fall 2%.
  6. Read the headline. On the defaults it is 5.0%, and the line under it gives the same slope as Ratio 1:20 · 2.9° · 0.60 in/ft. The next line repeats your rise and run so you can check what you typed.
  7. Read the check. The ramp line is for a ramp. The foundation line is for finished grade falling away from a building.
  8. Tap BASIS & WHAT WAS ASSUMED to see which code edition the two checks come from.

Reading the results

Grade / Slope scrolled down. The answer bar keeps 5.0% and the ramp check, cut off at the…. RESULTS shows the ratio and both green checks, then the BASIS & WHAT WAS ASSUMED row and the link Check before you cut · Measure twice. The GRADE PROFILE drawing shows SLOPE 5.0% (1:20), a dashed ADA 1:12 REF line, a 10' 0" run and a 6" rise, under the title strip GRADE PROFILE 5.0% (1:20) SLOPE NOT TO SCALE. Below it a dimmed SHARE PDF sits beside a lit SAVE, over the line Enter your own measurements to export. 11 12 14 15
The numbers match the list below.
  1. The headline is the slope in percent: rise over run. It is dimmed and tagged sample until you change an input.
  2. Ratio, degrees, in/ft. The ratio is rise to run, to one decimal, so 1:20 means one unit of fall in twenty of run and 1:1.5 is a steep bank. It is never rounded to a gentler slope. When the rise is longer than the run it reads the other way round, so 12' of rise in 5' of run is 2.4:1. With no rise at all it reads 1:∞ (flat). Inches per foot is the form most crews set a level or a string line to.
  3. Ramp check. Green reads Within 8.3% (1:12) max for the ramp at the egress door (IRC 2021 R311.8.1), or Within 12.5% (1:8) max for a ramp not at the egress door when RAMP SERVES is Other ramp. In red, EXCEEDS … means the slope is steeper than that line: make RUN longer or RISE smaller. A ramp steeper than 1:12 that passes as Other ramp adds Handrail on at least one side — steeper than 1:12 (IRC 2021 R311.8.3). For a bank or a swale, this line is not about your job: set PURPOSE to Drainage and it goes away.
  4. Drainage check. Green reads At least 5.0% grade away from the foundation (IRC 2021 R401.3), or At least 2.0% for paving within 10' of the foundation with SURFACE on Paved. In red, BELOW … means the ground or the paving is flatter than that line: increase RISE over the same run. A patio or walk against the house IS this line's job — set SURFACE to Paved. For a ramp, set PURPOSE to Ramp and it goes away.
  5. At a limit the slope and the limit gain a decimal, so a slope a hair over 1:12 reads 8.34% against 8.33%, never 8.3% against 8.3%.
  6. BASIS & WHAT WAS ASSUMED opens to IRC 2021 — verify local code, a note that states and towns amend the code, and that the 2024 IRC renumbers the ramp rules to R318.8 with the same 1:12 and 1:8. Check the edition your building department has adopted before you rely on either check.
  7. The drawing is the grade in profile with your rise and run on it and a dashed ADA 1:12 REF line to compare against. A ramp over its maximum is flagged in red on the drawing too. Pinch to zoom and use the expand button for full screen. See Drawings.
Grade / Slope is a Pro calculator. SHARE PDF and SAVE are Pro as well, a one-time purchase. SHARE PDF stays dim until you have entered your own measurements. SAVE stays lit, but until then a tap only answers Enter your job's numbers first and saves nothing.

Common mistakes