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IBU Calculator (Tinseth)

Computes the International Bitterness Units of a beer from up to 12 hop additions (weight, alpha-acid percentage, boil time) using Glenn Tinseth's utilization model, with a 10 % utilization bonus for pellet hops, and reports the BU:GU bitterness ratio.

Batch volume (L)Post-boil volume of wort in litres that the hops end up in (1 US gal = 3.785 L). Boil gravity (SG)Average specific gravity of the wort during the boil; for a full-volume boil use the original gravity, for a concentrated boil the (higher) gravity of the kettle wort. Hop weights (g)Weight of each hop addition in grams (1 oz = 28.35 g), in order. Alpha acid percentages (%)Alpha-acid content of each addition in percent (from the packet), same order as the weights. Boil times (min)Minutes each addition boils (0 for flame-out additions), same order. Hop form (optional)Pellets release alpha acids more readily; the model multiplies utilization by 1.10 for pellets. Original gravity (for BU:GU) (SG) (optional)Original gravity of the finished wort for the BU:GU ratio; defaults to boil_gravity.

When to use

You are designing or checking a homebrew recipe and need the predicted IBU for a hop schedule at a given batch size and boil gravity.

Do not use when: The bitterness comes from dry hopping, whirlpool or hop extracts (utilization models cover kettle additions only), or you need actual measured IBU (requires laboratory spectrophotometry).

Formula

U_i = 1.65 × 0.000125^(boil_gravity − 1) × (1 − e^(−0.04 × boil_time_i)) / 4.15 (× 1.10 for pellets); IBU_i = hop_weight_g_i × alpha_acid_percent_i / 100 × U_i × 1000 / batch_volume_l; total_ibu = Σ IBU_i; BU:GU = total_ibu / ((original_gravity − 1) × 1000)

Tinseth's utilization model (1997) was fitted to measured homebrew batches and is the one used by most recipe software; real utilization varies with kettle geometry, hop age and wort pH, and predictions above about 100 IBU exceed what can be measured. The 10 % pellet adjustment is common practice rather than part of the original model.

Inputs

Parameter	Type	Unit	Required	Description
`batch_volume_l`	number	L	yes	Post-boil volume of wort in litres that the hops end up in (1 US gal = 3.785 L). Range: > 0, ≤ 100000
`boil_gravity`	number	SG	yes	Average specific gravity of the wort during the boil; for a full-volume boil use the original gravity, for a concentrated boil the (higher) gravity of the kettle wort. Range: ≥ 1, ≤ 1.15
`hop_weights_g`	number_list	g	yes	Weight of each hop addition in grams (1 oz = 28.35 g), in order.
`alpha_acid_percents`	number_list	%	yes	Alpha-acid content of each addition in percent (from the packet), same order as the weights.
`boil_times_min`	number_list	min	yes	Minutes each addition boils (0 for flame-out additions), same order.
`hop_form`	enum: whole \| pellet		default whole	Pellets release alpha acids more readily; the model multiplies utilization by 1.10 for pellets.
`original_gravity`	number	SG	no	Original gravity of the finished wort for the BU:GU ratio; defaults to boil_gravity. Range: ≥ 1, ≤ 1.2

Outputs

Output	Type	Unit	Description
`total_ibu`	number	IBU	Sum of the IBU of all additions (mg of isomerized alpha acids per litre).
`additions`	list		Per hop addition: weight_g, alpha_acid_percent, boil_time_min, utilization_percent and ibu.
`bigness_factor`	number		Gravity term 1.65 × 0.000125^(boil_gravity − 1); higher gravity lowers utilization.
`bitterness_ratio`	number		total_ibu / ((original_gravity − 1) × 1000); below ≈ 0.3 reads malty, 0.3–0.6 balanced, above 0.6 hop-forward.
`style_note`	string		Descriptive bitterness level with typical styles at that IBU.

Example

20 L, 1.050, 30 g whole hops at 10 % for 60 min: {"batch_volume_l":20,"boil_gravity":1.05,"hop_weights_g":[30],"alpha_acid_percents":[10],"boil_times_min":[60],"hop_form":"whole"} → {"total_ibu":34.6,"bigness_factor":1.0528,"additions":[{"weight_g":30,"alpha_acid_percent":10,"boil_time_min":60,"utilization_percent":23.07,"ibu":34.6}],"bitterness_ratio":0.69}

23 L, 1.060, three pellet additions: {"batch_volume_l":23,"boil_gravity":1.06,"hop_weights_g":[40,25,30],"alpha_acid_percents":[6.5,5.5,5.5],"boil_times_min":[60,15,5],"hop_form":"pellet","original_gravity":1.06} → {"total_ibu":36.4,"additions":[{"ibu":26.22},{"ibu":6.88},{"ibu":3.32}],"bitterness_ratio":0.61}

GET https://tttkmbb.com/api/v1/calculate/ibu-tinseth?batch_volume_l=20&boil_gravity=1.05&hop_weights_g=30&alpha_acid_percents=10&boil_times_min=60&hop_form=whole

Machine access

API: GET https://tttkmbb.com/api/v1/calculate/ibu-tinseth (query parameters) or POST with a JSON body {"inputs": {...}}
Schema: https://tttkmbb.com/api/v1/calculators/ibu-tinseth · Markdown: https://tttkmbb.com/food/ibu-tinseth.md · JSON definition: https://tttkmbb.com/food/ibu-tinseth.json
MCP: server https://tttkmbb.com/mcp, tool run_calculator with calculator_id="ibu-tinseth"
OpenAPI operationId: calculate_ibu_tinseth
Freshness: static. Authentication: none. Rate limit: fair use (see rate limits).

Sources

FAQ

Which gravity do I enter for boil_gravity?

The average gravity of the wort while the hops are boiling. For a full-volume boil that is close to the original gravity; for a partial boil topped up with water afterwards, use the kettle gravity, which is higher and lowers utilization.

Why do other calculators (Rager, Garetz) give different IBU?

Each model was fitted to different data; Rager predicts 10–30 % more IBU than Tinseth for long boils. Always compare recipes using the same model.

How do I count whirlpool or flame-out hops?

Enter 0 minutes and they contribute nothing here, although hot-side steeping does add some bitterness; some brewers enter 5–10 minutes as a rough proxy.

Related calculators

Homebrew ABV Calculator — Alcohol content of the same recipe from gravity readings.
Beer Color (SRM) Calculator — Predict the beer colour from the grain bill.
Mass / Weight Converter — Convert hop weights between ounces and grams.